Spamihilator - The free Anti-Spam-Filter Spamihilator removes more than 98% of spam mails before they even get into your inbox.
imapsync - Console-based utility for migrating IMAP mailboxes.
Mailwasher - Over 8 million people use MailWasher as their spam filter
Gmvault - Backup the emails in your Gmail account.
SpamAssassin - Use this program to "Unspam" your mailbox(es).
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.