imapsync - Console-based utility for migrating IMAP mailboxes.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
Gmvault - Backup the emails in your Gmail account.
MailScanner - MailScanner is a open source email security system design for Linux-based email gateways.
Cryoserver - Cryoserver is an all-in-one email archiving solution that empowers you to preserve your email in a tamper-evident archive, making you transform your data into a useful archive for everyday use.
Rspamd - Rspamd is an advanced spam filtering system that allows evaluation of messages by a number of rules...