Lotame - Make your data actionable, learn about your most valuable customers, improve ROI by targeting the right audience and increase relevance across screens.

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.

Adobe Audience Manager - Adobe Audience Manager is a data management platform that integrates online and offline data to deliver a unified view of all your audiences

imapsync - Console-based utility for migrating IMAP mailboxes.

Google Audience Center - 3 votes and 6 comments so far on Reddit

Gmvault - Backup the emails in your Gmail account.