On Wed, 06 Jul 2011 20:46:48 +0200, Daniel Schoepe <daniel.schoepe@googlemail.com> wrote:
> One problem is that maildir doesn't support tags, so we would have to
> switch to a format that does or somehow store them in the maildir, in
> which case we would also have to adapt offlineimap or a similar tool to
> sync tags as well.

Right, Maildirs don't store them. AFAIK dovecot stores them in the
user-defined 'use-1-letter-abbrev-for-up-to-20-tags' notation or similar
for it's maildir. But there is no standard, and maildir is not the
answer. Either notmuch would have to directly interact via IMAP protocol
(outch), or some intermediary fetcher would have to store tags in some
type of database (which is what offlineimap could do at some point in
time).
 
> > Do you know what the status is of *server* support ? Because imo this *is* a
> > big deal, without real standardized server support an IMAP store for tags is
> > off the table.
> 
> Support for tags is mentioned in the RFC for IMAP, but it's optional. As
> far as I know, must servers today support them though.

I can't speak for Gmail, but all major servers, ie Cyrus, Dovecot, and
even Exchange seem to handle tags just fine.

Sebastian