GNU Mailutils is a rich and powerful protocol-independent mail framework. It contains a series of useful mail libraries, clients, and servers. These are the primary mail utilities for the GNU system. The central library is capable of handling electronic mail in various mailbox formats and protocols
... [More], both local and remote. Specifically, this project contains a POP3 server, an IMAP4 server, and a Sieve mail filter. It also provides a POSIX `mailx' client, and a collection of other handy tools.
The GNU Mailutils libraries supply an ample set of primitives for handling electronic mail in programs written in C, C++, Python or Scheme. [Less]