Comment 142 for bug 308181

(In reply to Hugo Osvaldo Barrera from comment #53)
> 4) Only thunderbird uses this information. If each email client had it's
> own non-standard mechanism, then ISPs would have a huge burden to update
> each of them with new information when they change their email server.

Evolution uses it too, although it looks like they host their own copy of the database. Check out:
http://git.gnome.org/browse/evolution/tree/mail/e-mail-autoconfig.c
which uses a (sadly non-SSL) base url of:
http://api.gnome.org/evolution/autoconfig/1.1/

The upcoming Firefox OS Gaia e-mail client also uses the ISP database too.

Note: Neither this nor I believe Ben's comments are meant to suggest that we don't want to support DNS SRV. Unfortunately, it's still a non-trivial undertaking to get the support in the gecko platform that has not been prioritized on the platform side. For Firefox OS v2 we are hoping to get it prioritized.