Zoho Mail - Zoho Mail is a secure, encrypted, and enterprise-ready email solution, a suite of apps tailor-made for your organization's needs.
imapsync - Console-based utility for migrating IMAP mailboxes.
FastMail - Email, calendars, and contacts to highest standards of security, privacy and reliability.
Gmvault - Backup the emails in your Gmail account.
Rackspace Email Hosting - Rackspace Email Hosting is a platform that provides business with web-hosted email services.
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.