Chapter 9. Configuring and maintaining a Dovecot IMAP and POP3 server Dovecot is a high-performance mail delivery agent (MDA) with a focus on security. You can use IMAP or POP3-compatible email clients to connect to a Dovecot server and read or download emails. Key features of Dovecot: The design and implementation focuses on security Two-way replication support for high availability to improve the performance in large environments Supports the high-performance dbox mailbox format, but also mbox and Maildir for compatibility reasons Self-healing features, such as fixing broken index files Compliance with the IMAP standards Workaround support to bypass bugs in IMAP and POP3 clients 9.1. Setting up a Dovecot server with PAM authentication Dovecot supports the Name Service Switch (NSS) interface as a user database and the Pluggable Authentication Modules (PAM) framework as an authentication backend. With this configuration, Dovecot can provide services to users who are available locally on the server through NSS. Use PAM authentication if accounts: Are defined locally in the /etc/passwd file Are stored in a remote database but they are available locally through the System Security Services Daemon (SSSD) or other NSS plugins. 9.1.1. Installing Dovecot The dovecot package provides: The dovecot service and the utilities to maintain it Services that Dovecot starts on demand, such as for authentication Plugins, such as server-side mail filtering Configuration files in the /etc/dovecot/ directory Documentation in the /usr/share/doc/dovecot/ directory Procedure Install the dovecot package: Note If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/ . step Configuring TLS encryption on a Dovecot server . 9.1.2. Configuring TLS encryption on a Dovecot server Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS). Prerequisites Dovecot is installed. The following files have been copied to the listed locations on the server: The server certificate: /etc/pki/dovecot/certs/server.example.com.crt The private key: /etc/pki/dovecot/private/server.example.com.key The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt The hostname in the Subject DN field of the server certificate matches the server's Fully-qualified Domain Name (FQDN). Procedure Set secure permissions on the private key file: Generate a file with Diffie-Hellman parameters: Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file: Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server's certificate and private key: Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: Important To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character. step Preparing Dovecot to use virtual users Additional resources /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt 9.1.3. Preparing Dovecot to use virtual users By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits: Dovecot performs file system actions as a specific local user instead of using the user's ID (UID). Users do not need to be available locally on the server. You can store all mailboxes and user-specific files in one root directory. Users do not require a UID and group ID (GID), which reduces administration efforts. Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files. Setting up replication is easier. Prerequisites Dovecot is installed. Procedure Create the vmail user: Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose. If you use a different path than /var/mail/ , set the mail_spool_t SELinux context on it, for example: Grant write permissions on /var/mail/ only to the vmail user: Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: With this setting: Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format. Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox. step Using PAM as the Dovecot authentication backend . Additional resources /usr/share/doc/dovecot/wiki/VirtualUsers.txt /usr/share/doc/dovecot/wiki/MailLocation.txt /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt /usr/share/doc/dovecot/wiki/Variables.txt 9.1.4. Using PAM as the Dovecot authentication backend By default, Dovecot uses the Name Service Switch (NSS) interface as the user database and the Pluggable Authentication Modules (PAM) framework as the authentication backend. Customize the settings to adapt Dovecot to your environment and to simplify administration by using the virtual users feature. Prerequisites Dovecot is installed. The virtual users feature is configured. Procedure Update the first_valid_uid parameter in the /etc/dovecot/conf.d/10-mail.conf file to define the lowest user ID (UID) that can authenticate to Dovecot: By default, users with a UID greater than or equal to 1000 can authenticate. If required, you can also set the last_valid_uid parameter to define the highest UID that Dovecot allows to log in. In the /etc/dovecot/conf.d/auth-system.conf.ext file, add the override_fields parameter to the userdb section as follows: Due to the fixed values, Dovecot does not query these settings from the /etc/passwd file. As a result, the home directory defined in /etc/passwd does not need to exist. step Complete the Dovecot configuration . Additional resources /usr/share/doc/dovecot/wiki/PasswordDatabase.PAM.txt /usr/share/doc/dovecot/wiki/VirtualUsers.Home.txt 9.1.5. Completing the Dovecot configuration Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server. Prerequisites The following has been configured in Dovecot: TLS encryption An authentication backend Clients trust the Certificate Authority (CA) certificate. Procedure If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: By default, the imap , pop3 , and lmtp protocols are enabled. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: Enable and start the dovecot service: Verification Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use: Table 9.1. Connection settings to the Dovecot server Protocol Port Connection security Authentication method IMAP 143 STARTTLS PLAIN [a] IMAPS 993 SSL/TLS PLAIN [a] POP3 110 STARTTLS PLAIN [a] POP3S 995 SSL/TLS PLAIN [a] [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed. Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS. Display configuration settings with non-default values: Additional resources firewall-cmd(1) man page on your system 9.2. Setting up a Dovecot server with LDAP authentication If your infrastructure uses an LDAP server to store accounts, you can authenticate Dovecot users against it. In this case, you manage accounts centrally in the directory and, users do not required local access to the file system on the Dovecot server. Centrally-managed accounts are also a benefit if you plan to set up multiple Dovecot servers with replication to make your mailboxes high available. 9.2.1. Installing Dovecot The dovecot package provides: The dovecot service and the utilities to maintain it Services that Dovecot starts on demand, such as for authentication Plugins, such as server-side mail filtering Configuration files in the /etc/dovecot/ directory Documentation in the /usr/share/doc/dovecot/ directory Procedure Install the dovecot package: Note If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/ . step Configuring TLS encryption on a Dovecot server . 9.2.2. Configuring TLS encryption on a Dovecot server Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS). Prerequisites Dovecot is installed. The following files have been copied to the listed locations on the server: The server certificate: /etc/pki/dovecot/certs/server.example.com.crt The private key: /etc/pki/dovecot/private/server.example.com.key The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt The hostname in the Subject DN field of the server certificate matches the server's Fully-qualified Domain Name (FQDN). Procedure Set secure permissions on the private key file: Generate a file with Diffie-Hellman parameters: Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file: Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server's certificate and private key: Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: Important To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character. step Preparing Dovecot to use virtual users Additional resources /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt 9.2.3. Preparing Dovecot to use virtual users By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits: Dovecot performs file system actions as a specific local user instead of using the user's ID (UID). Users do not need to be available locally on the server. You can store all mailboxes and user-specific files in one root directory. Users do not require a UID and group ID (GID), which reduces administration efforts. Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files. Setting up replication is easier. Prerequisites Dovecot is installed. Procedure Create the vmail user: Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose. If you use a different path than /var/mail/ , set the mail_spool_t SELinux context on it, for example: Grant write permissions on /var/mail/ only to the vmail user: Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: With this setting: Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format. Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox. step Using LDAP as the Dovecot authentication backend . Additional resources /usr/share/doc/dovecot/wiki/VirtualUsers.txt /usr/share/doc/dovecot/wiki/MailLocation.txt /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt /usr/share/doc/dovecot/wiki/Variables.txt 9.2.4. Using LDAP as the Dovecot authentication backend Users in an LDAP directory can usually authenticate themselves to the directory service. Dovecot can use this to authenticate users when they log in to the IMAP and POP3 services. This authentication method has a number of benefits, such as: Administrators can manage users centrally in the directory. The LDAP accounts do not require any special attributes. They only need to be able to authenticate to the LDAP server. Consequently, this method is independent from the password storage scheme used on the LDAP server. Users do not need to be available locally on the server through the Name Service Switch (NSS) interface and the Pluggable Authentication Modules (PAM) framework. Prerequisites Dovecot is installed. The virtual users feature is configured. Connections to the LDAP server support TLS encryption. RHEL on the Dovecot server trusts the Certificate Authority (CA) certificate of the LDAP server. If users are stored in different trees in the LDAP directory, a dedicated LDAP account for Dovecot exists to search the directory. This account requires permissions to search for Distinguished Names (DNs) of other users. Procedure Configure the authentication backends in the /etc/dovecot/conf.d/10-auth.conf file: Comment out include statements for auth-*.conf.ext authentication backend configuration files that you do not require, for example: Enable LDAP authentication by uncommenting the following line: Edit the /etc/dovecot/conf.d/auth-ldap.conf.ext file, and add the override_fields parameter as follows to the userdb section: Due to the fixed values, Dovecot does not query these settings from the LDAP server. Consequently, these attributes also do not have to be present. Create the /etc/dovecot/dovecot-ldap.conf.ext file with the following settings: Depending on the LDAP structure, configure one of the following: If users are stored in different trees in the LDAP directory, configure dynamic DN lookups: Dovecot uses the specified DN, password, and filter to search the DN of the authenticating user in the directory. In this search, Dovecot replaces %n in the filter with the username. Note that the LDAP search must return only one result. If all users are stored under a specific entry, configure a DN template: Enable authentication binds to the LDAP server to verify Dovecot users: Set the URL to the LDAP server: For security reasons, only use encrypted connections using LDAPS or the STARTTLS command over the LDAP protocol. For the latter, additionally add tls = yes to the settings. For a working certificate validation, the hostname of the LDAP server must match the hostname used in its TLS certificate. Enable the verification of the LDAP server's TLS certificate: Set the base DN to the DN where to start searching for users: Set the search scope: Dovecot searches with the onelevel scope only in the specified base DN and with the subtree scope also in subtrees. Set secure permissions on the /etc/dovecot/dovecot-ldap.conf.ext file: step Complete the Dovecot configuration . Additional resources /usr/share/doc/dovecot/example-config/dovecot-ldap.conf.ext /usr/share/doc/dovecot/wiki/UserDatabase.Static.txt /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.txt /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.AuthBinds.txt /usr/share/doc/dovecot/wiki/AuthDatabase.LDAP.PasswordLookups.txt 9.2.5. Completing the Dovecot configuration Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server. Prerequisites The following has been configured in Dovecot: TLS encryption An authentication backend Clients trust the Certificate Authority (CA) certificate. Procedure If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: By default, the imap , pop3 , and lmtp protocols are enabled. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: Enable and start the dovecot service: Verification Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use: Table 9.2. Connection settings to the Dovecot server Protocol Port Connection security Authentication method IMAP 143 STARTTLS PLAIN [a] IMAPS 993 SSL/TLS PLAIN [a] POP3 110 STARTTLS PLAIN [a] POP3S 995 SSL/TLS PLAIN [a] [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed. Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS. Display configuration settings with non-default values: Additional resources firewall-cmd(1) man page on your system 9.3. Setting up a Dovecot server with MariaDB SQL authentication If you store users and passwords in a MariaDB SQL server, you can configure Dovecot to use it as the user database and authentication backend. With this configuration, you manage accounts centrally in a database, and users have no local access to the file system on the Dovecot server. Centrally managed accounts are also a benefit if you plan to set up multiple Dovecot servers with replication to make your mailboxes highly available. 9.3.1. Installing Dovecot The dovecot package provides: The dovecot service and the utilities to maintain it Services that Dovecot starts on demand, such as for authentication Plugins, such as server-side mail filtering Configuration files in the /etc/dovecot/ directory Documentation in the /usr/share/doc/dovecot/ directory Procedure Install the dovecot package: Note If Dovecot is already installed and you require clean configuration files, rename or remove the /etc/dovecot/ directory. Afterwards, reinstall the package. Without removing the configuration files, the yum reinstall dovecot command does not reset the configuration files in /etc/dovecot/ . step Configuring TLS encryption on a Dovecot server . 9.3.2. Configuring TLS encryption on a Dovecot server Dovecot provides a secure default configuration. For example, TLS is enabled by default to transmit credentials and data encrypted over networks. To configure TLS on a Dovecot server, you only need to set the paths to the certificate and private key files. Additionally, you can increase the security of TLS connections by generating and using Diffie-Hellman parameters to provide perfect forward secrecy (PFS). Prerequisites Dovecot is installed. The following files have been copied to the listed locations on the server: The server certificate: /etc/pki/dovecot/certs/server.example.com.crt The private key: /etc/pki/dovecot/private/server.example.com.key The Certificate Authority (CA) certificate: /etc/pki/dovecot/certs/ca.crt The hostname in the Subject DN field of the server certificate matches the server's Fully-qualified Domain Name (FQDN). Procedure Set secure permissions on the private key file: Generate a file with Diffie-Hellman parameters: Depending on the hardware and entropy on the server, generating Diffie-Hellman parameters with 4096 bits can take several minutes. Set the paths to the certificate and private key files in the /etc/dovecot/conf.d/10-ssl.conf file: Update the ssl_cert and ssl_key parameters, and set them to use the paths of the server's certificate and private key: Uncomment the ssl_ca parameter, and set it to use the path to the CA certificate: Uncomment the ssl_dh parameter, and set it to use the path to the Diffie-Hellman parameters file: Important To ensure that Dovecot reads the value of a parameter from a file, the path must start with a leading < character. step Preparing Dovecot to use virtual users Additional resources /usr/share/doc/dovecot/wiki/SSL.DovecotConfiguration.txt 9.3.3. Preparing Dovecot to use virtual users By default, Dovecot performs many actions on the file system as the user who uses the service. However, configuring the Dovecot back end to use one local user to perform these actions has several benefits: Dovecot performs file system actions as a specific local user instead of using the user's ID (UID). Users do not need to be available locally on the server. You can store all mailboxes and user-specific files in one root directory. Users do not require a UID and group ID (GID), which reduces administration efforts. Users who have access to the file system on the server cannot compromise their mailboxes or indexes because they cannot access these files. Setting up replication is easier. Prerequisites Dovecot is installed. Procedure Create the vmail user: Dovecot will later use this user to manage the mailboxes. For security reasons, do not use the dovecot or dovenull system users for this purpose. If you use a different path than /var/mail/ , set the mail_spool_t SELinux context on it, for example: Grant write permissions on /var/mail/ only to the vmail user: Uncomment the mail_location parameter in the /etc/dovecot/conf.d/10-mail.conf file, and set it to the mailbox format and location: With this setting: Dovecot uses the high-performant dbox mailbox format in single mode. In this mode, the service stores each mail in a separate file, similar to the maildir format. Dovecot resolves the %n variable in the path to the username. This is required to ensure that each user has a separate directory for its mailbox. step Using a MariaDB SQL database as the Dovecot authentication backend Additional resources /usr/share/doc/dovecot/wiki/VirtualUsers.txt /usr/share/doc/dovecot/wiki/MailLocation.txt /usr/share/doc/dovecot/wiki/MailboxFormat.dbox.txt /usr/share/doc/dovecot/wiki/Variables.txt 9.3.4. Using a MariaDB SQL database as the Dovecot authentication backend Dovecot can read accounts and passwords from a MariaDB database and use it to authenticate users when they log in to the IMAP or POP3 service. The benefits of this authentication method include: Administrators can manage users centrally in a database. Users have no access locally on the server. Prerequisites Dovecot is installed. The virtual users feature is configured. Connections to the MariaDB server support TLS encryption. The dovecotDB database exists in MariaDB, and the users table contains at least a username and password column. The password column contains passwords encrypted with a scheme that Dovecot supports. The passwords either use the same scheme or have a { pw-storage-scheme } prefix. The dovecot MariaDB user has read permission on the users table in the dovecotDB database. The certificate of the Certificate Authority (CA) that issued the MariaDB server's TLS certificate is stored on the Dovecot server in the /etc/pki/tls/certs/ca.crt file. Procedure Install the dovecot-mysql package: Configure the authentication backends in the /etc/dovecot/conf.d/10-auth.conf file: Comment out include statements for auth-*.conf.ext authentication backend configuration files that you do not require, for example: Enable SQL authentication by uncommenting the following line: Edit the /etc/dovecot/conf.d/auth-sql.conf.ext file, and add the override_fields parameter to the userdb section as follows: Due to the fixed values, Dovecot does not query these settings from the SQL server. Create the /etc/dovecot/dovecot-sql.conf.ext file with the following settings: To use TLS encryption to the database server, set the ssl_ca option to the path of the certificate of the CA that issued the MariaDB server certificate. For a working certificate validation, the hostname of the MariaDB server must match the hostname used in its TLS certificate. If the password values in the database contain a { pw-storage-scheme } prefix, you can omit the default_pass_scheme setting. The queries in the file must be set as follows: For the user_query parameter, the query must return the username of the Dovecot user. The query must also return only one result. For the password_query parameter, the query must return the username and the password, and Dovecot must use these values in the user and password variables. Therefore, if the database uses different column names, use the AS SQL command to rename a column in the result. For the iterate_query parameter, the query must return a list of all users. Set secure permissions on the /etc/dovecot/dovecot-sql.conf.ext file: step Complete the Dovecot configuration . Additional resources /usr/share/doc/dovecot/example-config/dovecot-sql.conf.ext /usr/share/doc/dovecot/wiki/Authentication.PasswordSchemes.txt 9.3.5. Completing the Dovecot configuration Once you have installed and configured Dovecot, open the required ports in the firewalld service, and enable and start the service. Afterwards, you can test the server. Prerequisites The following has been configured in Dovecot: TLS encryption An authentication backend Clients trust the Certificate Authority (CA) certificate. Procedure If you want to provide only an IMAP or POP3 service to users, uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to the required protocols. For example, if you do not require POP3, set: By default, the imap , pop3 , and lmtp protocols are enabled. Open the ports in the local firewall. For example, to open the ports for the IMAPS, IMAP, POP3S, and POP3 protocols, enter: Enable and start the dovecot service: Verification Use a mail client, such as Mozilla Thunderbird, to connect to Dovecot and read emails. The settings for the mail client depend on the protocol you want to use: Table 9.3. Connection settings to the Dovecot server Protocol Port Connection security Authentication method IMAP 143 STARTTLS PLAIN [a] IMAPS 993 SSL/TLS PLAIN [a] POP3 110 STARTTLS PLAIN [a] POP3S 995 SSL/TLS PLAIN [a] [a] The client transmits data encrypted through the TLS connection. Consequently, credentials are not disclosed. Note that this table does not list settings for unencrypted connections because, by default, Dovecot does not accept plain text authentication on connections without TLS. Display configuration settings with non-default values: Additional resources firewall-cmd(1) man page on your system 9.4. Configuring replication between two Dovecot servers With two-way replication, you can make your Dovecot server high-available, and IMAP and POP3 clients can access a mailbox on both servers. Dovecot keeps track of changes in the index logs of each mailbox and solves conflicts in a safe way. Perform this procedure on both replication partners. Note Replication works only between server pairs. Consequently, in a large cluster, you need multiple independent backend pairs. Prerequisites Both servers use the same authentication backend. Preferably, use LDAP or SQL to maintain accounts centrally. The Dovecot user database configuration supports user listing. Use the doveadm user '*' command to verify this. Dovecot accesses mailboxes on the file system as the vmail user instead of the user's ID (UID). Procedure Create the /etc/dovecot/conf.d/10-replication.conf file and perform the following steps in it: Enable the notify and replication plug-ins: Add a service replicator section: With these settings, Dovecot starts at least one replicator process when the dovecot service starts. Additionally, this section defines the settings on the replicator-doveadm socket. Add a service aggregator section to configure the replication-notify-fifo pipe and replication-notify socket: Add a service doveadm section to define the port of the replication service: Set the password of the doveadm replication service: The password must be the same on both servers. Configure the replication partner: Optional: Define the maximum number of parallel dsync processes: The default value of replication_max_conns is 10 . Set secure permissions on the /etc/dovecot/conf.d/10-replication.conf file: Enable the nis_enabled SELinux Boolean to allow Dovecot to open the doveadm replication port: Configure firewalld rules to allow only the replication partner to access the replication port, for example: The subnet masks /32 for the IPv4 and /128 for the IPv6 address limit the access to the specified addresses. Perform this procedure also on the other replication partner. Reload Dovecot: Verification Perform an action in a mailbox on one server and then verify if Dovecot has replicated the change to the other server. Display the replicator status: Display the replicator status of a specific user: Additional resources dsync(1) man page on your system /usr/share/doc/dovecot/wiki/Replication.txt 9.5. Automatically subscribing users to IMAP mailboxes Typically, IMAP server administrators want Dovecot to automatically create certain mailboxes, such as Sent and Trash , and subscribe the users to them. You can set this in the configuration files. Additionally, you can define special-use mailboxes . IMAP clients often support defining mailboxes for special purposes, such as for sent emails. To avoid that the user has to manually select and set the correct mailboxes, IMAP servers can send a special-use attribute in the IMAP LIST command. Clients can then use this attribute to identify and set, for example, the mailbox for sent emails. Prerequisites Dovecot is configured. Procedure Update the inbox namespace section in the /etc/dovecot/conf.d/15-mailboxes.conf file: Add the auto = subscribe setting to each special-use mailbox that should be available to users, for example: If your mail clients support more special-use mailboxes, you can add similar entries. The special_use parameter defines the value that Dovecot sends in the special-use attribute to the clients. Optional: If you want to define other mailboxes that have no special purpose, add mailbox sections for them in the user's inbox, for example: You can set the auto parameter to one of the following values: subscribe : Automatically creates the mailbox and subscribes the user to it. create : Automatically creates the mailbox without subscribing the user to it. no (default): Dovecot neither creates the mailbox nor does it subscribe the user to it. Reload Dovecot: Verification Use an IMAP client and access your mailbox. Mailboxes with the setting auto = subscribe are automatically visible. If the client supports special-use mailboxes and the defined purposes, the client automatically uses them. Additional resources RFC 6154: IMAP LIST Extension for Special-Use Mailboxes /usr/share/doc/dovecot/wiki/MailboxSettings.txt 9.6. Configuring an LMTP socket and LMTPS listener SMTP servers, such as Postfix, use the Local Mail Transfer Protocol (LMTP) to deliver emails to Dovecot. If the SMTP server runs: On the same host as Dovecot, use an LMTP socket On a different host, use an LMTP service By default, the LMTP protocol is not encrypted. However, if you configured TLS encryption, Dovecot uses the same settings automatically for the LMTP service. SMTP servers can then connect to it using the LMTPS protocol or the STARTTLS command over LMTP. Prerequisites Dovecot is installed. If you want to configure an LMTP service, TLS encryption is configured in Dovecot. Procedure Verify that the LMTP protocol is enabled: The protocol is enabled, if the output contains lmtp . If the lmtp protocol is disabled, edit the /etc/dovecot/dovecot.conf file, and append lmtp to the values in the protocols parameter: Depending on whether you need an LMTP socket or service, make the following changes in the service lmtp section in the /etc/dovecot/conf.d/10-master.conf file: LMTP socket: By default, Dovecot automatically creates the /var/run/dovecot/lmtp socket. Optional: Customize the ownership and permissions: LMTP service: Add a inet_listener sub-section: Configure firewalld rules to allow only the SMTP server to access the LMTP port, for example: The subnet masks /32 for the IPv4 and /128 for the IPv6 address limit the access to the specified addresses. Reload Dovecot: Verification If you configured the LMTP socket, verify that Dovecot has created the socket and that the permissions are correct: Configure the SMTP server to submit emails to Dovecot using the LMTP socket or service. When you use the LMTP service, ensure that the SMTP server uses the LMTPS protocol or sends the STARTTLS command to use an encrypted connection. Additional resources /usr/share/doc/dovecot/wiki/LMTP.txt 9.7. Disabling the IMAP or POP3 service in Dovecot By default, Dovecot provides IMAP and POP3 services. If you require only one of them, you can disable the other to reduce the surface for attack. Prerequisites Dovecot is installed. Procedure Uncomment the protocols parameter in the /etc/dovecot/dovecot.conf file, and set it to use the required protocols. For example, if you do not require POP3, set: By default, the imap , pop3 , and lmtp protocols are enabled. Reload Dovecot: Close the ports that are no longer required in the local firewall. For example, to close the ports for the POP3S and POP3 protocols, enter: Verification Display all ports in LISTEN mode opened by the dovecot process: In this example, Dovecot listens only on the TCP ports 993 (IMAPS) and 143 (IMAP). Note that Dovecot only opens a port for the LMTP protocol if you configure the service to listen on a port instead of using a socket. Additional resources firewall-cmd(1) man page on your system 9.8. Enabling server-side email filtering using Sieve on a Dovecot IMAP server You can upload Sieve scripts to a server using the ManageSieve protocol. Sieve scripts define rules and actions that a server should validate and perform on incoming emails. For example, users can use Sieve to forward emails from a specific sender, and administrators can create a global filter to move mails flagged by a spam filter into a separate IMAP folder. The ManageSieve plugin adds support for Sieve scripts and the ManageSieve protocol to a Dovecot IMAP server. Warning Use only clients that support using the ManageSieve protocol over TLS connections. Disabling TLS for this protocol causes clients to send credentials in plain text over the network. Prerequisites Dovecot is configured and provides IMAP mailboxes. TLS encryption is configured in Dovecot. The mail clients support the ManageSieve protocol over TLS connections. Procedure Install the dovecot-pigeonhole package: Uncomment the following line in /etc/dovecot/conf.d/20-managesieve.conf to enable the sieve protocol: This setting activates Sieve in addition to the other protocols that are already enabled. Open the ManageSieve port in firewalld : Reload Dovecot: Verification Use a client and upload a Sieve script. Use the following connection settings: Port: 4190 Connection security: SSL/TLS Authentication method: PLAIN Send an email to the user who has the Sieve script uploaded. If the email matches the rules in the script, verify that the server performs the defined actions. Additional resources /usr/share/doc/dovecot/wiki/Pigeonhole.Sieve.Plugins.IMAPSieve.txt /usr/share/doc/dovecot/wiki/Pigeonhole.Sieve.Troubleshooting.txt firewall-cmd(1) man page on your system 9.9. How Dovecot processes configuration files The dovecot package provides the main configuration file /etc/dovecot/dovecot.conf and multiple configuration files in the /etc/dovecot/conf.d/ directory. Dovecot combines the files to build the configuration when you start the service. The main benefit of multiple config files is to group settings and increase readability. If you prefer a single configuration file, you can instead maintain all settings in /etc/dovecot/dovecot.conf and remove all include and include_try statements from that file. Additional resources /usr/share/doc/dovecot/wiki/ConfigFile.txt /usr/share/doc/dovecot/wiki/Variables.txt

Commands:
yum install dovecot
chown root:root /etc/pki/dovecot/private/server.example.com.key chmod 600 /etc/pki/dovecot/private/server.example.com.key
openssl dhparam -out /etc/dovecot/dh.pem 4096
ssl_cert = < /etc/pki/dovecot/certs/server.example.com.crt ssl_key = < /etc/pki/dovecot/private/server.example.com.key
ssl_ca = < /etc/pki/dovecot/certs/ca.crt
ssl_dh = < /etc/dovecot/dh.pem
useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail
semanage fcontext -a -t mail_spool_t " <path> (/.*)?" restorecon -Rv <path>
chown vmail:vmail /var/mail/ chmod 700 /var/mail/
mail_location = sdbox : /var/mail/%n/
first_valid_uid = 1000
userdb { driver = passwd override_fields = uid= vmail gid= vmail home= /var/mail/%n/ }
protocols = imap lmtp
firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3 firewall-cmd --reload
systemctl enable --now dovecot
doveconf -n
yum install dovecot
chown root:root /etc/pki/dovecot/private/server.example.com.key chmod 600 /etc/pki/dovecot/private/server.example.com.key
openssl dhparam -out /etc/dovecot/dh.pem 4096
ssl_cert = < /etc/pki/dovecot/certs/server.example.com.crt ssl_key = < /etc/pki/dovecot/private/server.example.com.key
ssl_ca = < /etc/pki/dovecot/certs/ca.crt
ssl_dh = < /etc/dovecot/dh.pem
useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail
semanage fcontext -a -t mail_spool_t " <path> (/.*)?" restorecon -Rv <path>
chown vmail:vmail /var/mail/ chmod 700 /var/mail/
mail_location = sdbox : /var/mail/%n/
#!include auth-system.conf.ext
!include auth-ldap.conf.ext
userdb { driver = ldap args = /etc/dovecot/dovecot-ldap.conf.ext override_fields = uid= vmail gid= vmail home= /var/mail/%n/ }
dn = cn= dovecot_LDAP ,dc=example,dc=com dnpass = password pass_filter = (&(objectClass=posixAccount)(uid=%n))
auth_bind_userdn = cn=%n,ou=People,dc=example,dc=com
auth_bind = yes
uris = ldaps://LDAP-srv.example.com
tls_require_cert = hard
base = ou=People,dc=example,dc=com
scope = onelevel
chown root:root /etc/dovecot/dovecot-ldap.conf.ext chmod 600 /etc/dovecot/dovecot-ldap.conf.ext
protocols = imap lmtp
firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3 firewall-cmd --reload
systemctl enable --now dovecot
doveconf -n
yum install dovecot
chown root:root /etc/pki/dovecot/private/server.example.com.key chmod 600 /etc/pki/dovecot/private/server.example.com.key
openssl dhparam -out /etc/dovecot/dh.pem 4096
ssl_cert = < /etc/pki/dovecot/certs/server.example.com.crt ssl_key = < /etc/pki/dovecot/private/server.example.com.key
ssl_ca = < /etc/pki/dovecot/certs/ca.crt
ssl_dh = < /etc/dovecot/dh.pem
useradd --home-dir /var/mail/ --shell /usr/sbin/nologin vmail
semanage fcontext -a -t mail_spool_t " <path> (/.*)?" restorecon -Rv <path>
chown vmail:vmail /var/mail/ chmod 700 /var/mail/
mail_location = sdbox : /var/mail/%n/
yum install dovecot-mysql
#!include auth-system.conf.ext
!include auth-sql.conf.ext
userdb { driver = sql args = /etc/dovecot/dovecot-sql.conf.ext override_fields = uid= vmail gid= vmail home= /var/mail/%n/ }
driver = mysql connect = host= mariadb_srv.example.com dbname= dovecotDB user= dovecot password= dovecotPW ssl_ca= /etc/pki/tls/certs/ca.crt default_pass_scheme = SHA512-CRYPT user_query = SELECT username FROM users WHERE username ='%u'; password_query = SELECT username AS user, password FROM users WHERE username ='%u'; iterate_query = SELECT username FROM users ;
chown root:root /etc/dovecot/dovecot-sql.conf.ext chmod 600 /etc/dovecot/dovecot-sql.conf.ext
protocols = imap lmtp
firewall-cmd --permanent --add-service=imaps --add-service=imap --add-service=pop3s --add-service=pop3 firewall-cmd --reload
systemctl enable --now dovecot
doveconf -n
mail_plugins = USDmail_plugins notify replication
service replicator { process_min_avail = 1 unix_listener replicator-doveadm { mode = 0600 user = vmail } }
service aggregator { fifo_listener replication-notify-fifo { user = vmail } unix_listener replication-notify { user = vmail } }
service doveadm { inet_listener { port = 12345 } }
doveadm_password = replication_password
plugin { mail_replica = tcp: server2.example.com : 12345 }
replication_max_conns = 20
chown root:root /etc/dovecot/conf.d/10-replication.conf chmod 600 /etc/dovecot/conf.d/10-replication.conf
setsebool -P nis_enabled on
firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv4" source address=" 192.0.2.1/32 " port protocol="tcp" port=" 12345 " accept" firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv6" source address=" 2001:db8:2::1/128 " port protocol="tcp" port=" 12345 " accept" firewall-cmd --reload
systemctl reload dovecot
doveadm replicator status Queued 'sync' requests 0 Queued 'high' requests 0 Queued 'low' requests 0 Queued 'failed' requests 0 Queued 'full resync' requests 30 Waiting 'failed' requests 0 Total number of known users 75
doveadm replicator status example_user username priority fast sync full sync success sync failed example_user none 02:05:28 04:19:07 02:05:28 -
namespace inbox { mailbox Drafts { special_use = \Drafts auto = subscribe } mailbox Junk { special_use = \Junk auto = subscribe } mailbox Trash { special_use = \Trash auto = subscribe } mailbox Sent { special_use = \Sent auto = subscribe } }
namespace inbox { mailbox " Important Emails " { auto = <value> } }
systemctl reload dovecot
doveconf -a | egrep "^protocols" protocols = imap pop3 lmtp
protocols = ... lmtp
service lmtp { unix_listener lmtp { mode = 0600 user = postfix group = postfix } }
service lmtp { inet_listener lmtp { port = 24 } }
firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv4" source address=" 192.0.2.1/32 " port protocol="tcp" port=" 24 " accept" firewall-cmd --permanent --zone=public --add-rich-rule="rule family="ipv6" source address=" 2001:db8:2::1/128 " port protocol="tcp" port=" 24 " accept" firewall-cmd --reload
systemctl reload dovecot
ls -l /var/run/dovecot/lmtp s rw------- . 1 postfix postfix 0 Nov 22 17:17 /var/run/dovecot/lmtp
protocols = imap lmtp
systemctl reload dovecot
firewall-cmd --remove-service=pop3s --remove-service=pop3 firewall-cmd --reload
ss -tulp | grep dovecot tcp LISTEN 0 100 0.0.0.0:993 0.0.0.0:* users:(("dovecot",pid= 1405 ,fd= 44 )) tcp LISTEN 0 100 0.0.0.0:143 0.0.0.0:* users:(("dovecot",pid= 1405 ,fd= 42 )) tcp LISTEN 0 100 [::]:993 [::]:* users:(("dovecot",pid= 1405 ,fd= 45 )) tcp LISTEN 0 100 [::]:143 [::]:* users:(("dovecot",pid= 1405 ,fd= 43 ))
yum install dovecot-pigeonhole
protocols = USDprotocols sieve
firewall-cmd --permanent --add-service=managesieve firewall-cmd --reload
systemctl reload dovecot