Mail(1).
Fetchmail supports all standard mail-retrieval protocols in use on the
-Internet: POP3 (including some variants such as RPOP, APOP, KPOP), IMAP4rev1
+Internet: POP3 (including some variants such as APOP, KPOP), IMAP4rev1
(also IMAP4, IMAP2bis), IMAP4, ETRN, and ODMR. On the output side,
fetchmail supports ESMTP/SMTP, LMTP, and invocation of a local delivery agent.