ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
imapsync - Console-based utility for migrating IMAP mailboxes.
Enigmail - Security extension to Mozilla Thunderbird and SeaMonkey
Gmvault - Backup the emails in your Gmail account.
Skizzle Email - Skizzle is the most secure way to share end-to-end encrypted files through email, backed by blockchain
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.