Their configurations are specific, and used in many domains which we don't currently autodetect particularly well.

In which ways specific? Can't we just do DNS MX on the domain, notice that gmail.com is MX, and then do a lookup on gmail.com, i.e. the generic custom domain algo?

I've heard from some Google Apps users that it's a little more complicated than that, but I don't have the details at hand. (And even if it is that simple, we can probably shortcut it by just returning the gmail config if we see that gmail.com is the MX.)

I'd like to avoid any provider-specific hacks.

I would normally like to avoid provider-specific hacks, but if the provider is large enough, I think it might be in our best interest to have some. (I'ld also like everyone to use IMAP over SSL, and some sort of spam-proof version of SMTP, but I don't rule the world quite yet. ;) Finally, keep in mind that this code would be living off in a separate process somewhere, and wouldn't clutter either the ISPDB, or the autoconfig code bases.

Do you have an example domain for Google apps?

I've heard that sky.com uses Google Apps for their domain.

Thanks. dig mx sky.com: sky.com. 258 IN MX 5 alt1.aspmx.l.google.com. sky.com. 258 IN MX 5 alt2.aspmx.l.google.com. sky.com. 258 IN MX 10 aspmx2.googlemail.com. sky.com. 258 IN MX 10 aspmx3.googlemail.com. sky.com. 258 IN MX 10 aspmx4.googlemail.com. sky.com. 258 IN MX 1 aspmx.l.google.com. So, our generic DNX MX algo should work for it. I don't see any need to special-case Google Apps.

xref bug 342242