Fetchmail – a full-featured, robust, well-documented remote-mail retrieval and forwarding utility intended to be used over on-demand TCP/IP links (such as SLIP or PPP connections). It supports every remote-mail protocol now in use on the Internet: POP2, POP3, RPOP, APOP, KPOP, all flavors of IMAP, ETRN, and ODMR. It can even support IPv6 and IPSEC.
Fetchmail retrieves mail from remote mail servers and forwards it via SMTP, so it can then be read by normal mail user agents such as mutt, elm(1) or BSD Mail. It allows all your system MTA’s filtering, forwarding, and aliasing facilities to work just as they would on normal mail.
Fetchmail offers better protection against password-sniffing than any other Unix remote-mail client. It supports APOP, KPOP, OTP, Compuserve RPA, Microsoft NTLM, and IMAP RFC1731 encrypted authentication methods including CRAM-MD5 to avoid sending passwords en clair. It can be configured to support end-to-end encryption via tunneling with ssh, the Secure Shell.
Fetchmail can be used as a POP/IMAP-to-SMTP gateway for an entire DNS domain, collecting mail from a single drop box on an ISP and SMTP-forwarding it based on header addresses. (We don’t really recommend this, though, as it may lose important envelope-header information. ETRN or a UUCP connection is better.)
The original author of Fetchmail is Eric S. Raymond.