V12 Data - V12 Data offers rich data sets with verified addresses and emails for personalized marketing campaigns.
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
Gmvault - Backup the emails in your Gmail account.
Google Audience Center - 3 votes and 6 comments so far on Reddit
imapsync - Console-based utility for migrating IMAP mailboxes.