Is atomic MOVING of messages between IMAP folders possible?

[Timo Sirainen]

On 04 Aug 2014, at 14:12, Greg Sullivan <greg.sullivan at sullivang.net> wrote:

> Yes, both client and server support IMAP MOVE, and both also support
> CONDSTORE.
> 
> I have tried both with and without CONDSTORE enabled in the client, with
> the same result.

With CONDSTORE I was thinking you could do it something like:

1 FETCH 1 (FLAGS MODSEQ)
* 1 FLAGS () MODSEQ 12345
2 STORE (UNCHANGEDSINCE 12345) 1 +FLAGS $AtomicMove
3 MOVE 1 elsewhere

If another client attempts the same, either 1 will return $AtomicMove in flags -> abort or 2 will fail with NO. But you should still handle failures if the client/connection dies between 2 and 3 or 3 fails for some reason.

But, of course if you can't change the client code to do this then it doesn't help.

> I am very confident IMAP MOVE is actually being invoked, because
> intra-account moves occur extremely rapidly. (much faster than
> inter-account moves, which of course is a copy & delete)

Inter-account physically copies the data (FETCH + APPEND + EXPUNGE). Alternative to MOVE is COPY + EXPUNGE, which is just as fast as MOVE. Dovecot actually implements MOVE by internally doing a COPY + EXPUNGE.