FastMail - Email, calendars, and contacts to highest standards of security, privacy and reliability.

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.

Spark Mail - Spark helps you take your inbox under control. Instantly see what’s important and quickly clean up the rest. Spark for Teams allows you to create, discuss, and share email with your colleagues

Gmvault - Backup the emails in your Gmail account.

BlueMail - BlueMail is an email management app for Android, iOS, and Windows.

imapsync - Console-based utility for migrating IMAP mailboxes.