IMAP Transfer Tool

[ScottPeterJohnson]

(This issue was imported from Gitea) Scott on February 28, 2019: A seamless way to transfer/backup large volumes of mail, configurable via web interface. Proposed feature set:

• [x] One-off syncs between any two IMAP mailboxes (don't have to be Purelymail accounts).
• [ ] Schedule syncs, to e.g. use Purelymail as backup.

[dxtr]

I vote for the second task here!