Postbox — Awesome Email. I was never really enthusiastic about Thunderbird, so the announcement that it would no longer be developed didn't bother me much. But the fact that Sparrow now belongs to Google and, according to the announcements, nothing more is to be expected from it, really annoyed me - it was one of the faster clients for gmail and also had usable feature support for it. The Apple Mail client is rather stiff in comparison. Postbox claims to support gmail features, so it might be worth a try if Sparrow can no longer be used reliably due to bit rot.