On Mon, 11 Jul 2011 15:22:24 +0200, Sebastian Spaeth <Sebastian@sspaeth.de> wrote:
> > 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.

I just realized that this was a quite misleading typo, that should have
read "As far as I know, _most_ servers today support them though". 

I'd be very suprised if Gmail didn't support them. And even if not, one
could work around that by having a hypothetical tag synchroniser handle
Gmail differently and use their tagging mechanism:

http://code.google.com/apis/gmail/imap/#x-gm-labels

This would also have the added benefit of notmuch tags showing up in the
other gmail-tag-aware applications, like the web-interface.

Another issue brought up by DraX on IRC is that IMAP keywords don't
handle unicode. (Although the RFC specifies that every character except
some excluded special characters are allowed, so I guess it's
implementation-dependent).

I think the best way to go would be to extend both maildir and
offlineimap somehow to store tags and then store them as IMAP keywords /
gmail-labels in the case of Gmail on the server.

Cheers,
Daniel