Claws Mail is an email client, which means it retrieves and sends emails from and to your email server. It supports various protocols such as POP3 and IMAP for retrieving emails, and SMTP for sending emails.  When you set up your email account in Claws Mail, you provide the server details and your login credentials. Claws Mail then connects to your email server to fetch your emails, which are displayed in the client's interface. You can read, reply to, and organize these emails directly from the client. Claws Mail is known for its high level of customization and extensive features. It supports various plugins that extend its functionality, including spam filtering, email archiving, and more. It also allows you to customize its appearance with different themes. Moreover, Claws Mail uses a robust and efficient storage format (MH Maildir) that stores each email as a separate file, allowing for fast access and manipulation of individual messages.