Mail delivery agents

software that routes e-mail to its destination

Fetchmail is an open-source software utility for POSIX-compliant operating systems which is used to retrieve e-mail from a remote POP3, IMAP, or ODMR mail server to the user's local system. It was developed from the popclient program, written by Carl Harris.

procmail is an email server software component — specifically, a message delivery agent (MDA). It was one of the earliest mail filter programs. It is typically used in Unix-like mail systems, using the mbox and Maildir storage formats.