imapsync is en email IMAP tool for syncing, copying, migrating and archiving email mailboxes between two IMAP servers, one way, and without duplicates.
Question directly related to imapsync installation, usage, or problems can have this tag. Questions about imap transfers also.
To learn more, imapsync sites are https://imapsync.lamiral.info/ and https://github.com/imapsync/imapsync
IMAP, the Internet Message Access Protocol, is described at https://en.wikipedia.org/wiki/Internet_Message_Access_Protocol