Some Linux distributions give you a choice of mail packages, whereas others default to one particular type. During the installation, most Linux setup procedures will install the software properly except for some configuration information about the network. The transport is the low-level software that takes care of delivering the mail, both locally and across other machines. Users never work with the transport, although system administrators must configure it and understand the basic principles. The mailer is the user interface that presents mail to the user and accepts new mail.
Many mailers are available.
Mail Transport Agents Transport agents are the underlying software that connects your local machine to remote systems. You can find sendmail on the CD that accompanies this book. The configuration changes needed to set up smail or sendmail on your Linux system depend on the type of connection you have to the outside world. When this is added, any outgoing mail gets sent automatically when using a mailer like elm. The sendmail program is quite popular with small Linux installations.