Super outil pour transférer des mails d'une boite à une autre, notamment pour les migrations. Et il existe une image sur dockerhub (https://hub.docker.com/r/gilleslamiral/imapsync) dont la source est donnée si on a pas confiance, pour la builder soi-même en local.

docker run imapsync imapsync --dry \
--host1 domain.tld --user1 mailbox1@domain.tld --password1 password1 \
--host2 domain.tld --user2 mailbox2@domain.tld --password2 password2 --delete2

Il y a aussi ce très bon script python pour sauvegarder une boite en fichiers mbox : https://github.com/rcarmo/imapbackup

"""
To bring the world our unique end-to-end encrypted protocol and architecture that is the 'next-generation' of private and secure email. As founding partners of The Dark Mail Technical Alliance, both Silent Circle and Lavabit will work to bring other members into the alliance, assist them in implementing the new protocol and jointly work to proliferate the world's first end-to-end encrypted 'Email 3.0' throughout the world's email providers. Our goal is to open source the protocol and architecture and help others implement this new technology to address privacy concerns against surveillance and back door threats of any kind.
"""

via http://book.knah-tsaeb.org/?fwmb5w

premier jet pour les spécifications de Caliop.
TL;DR;