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
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Tutanota - Get your encrypted mailbox for free.
audriga Email and Groupware migration - Easily migrate your email, contacts, calendar items and tasks to your new provider or server. No software installation is required.