Been using Rackspace hosted email for a year now. One thing I can be certain: fantastic support! Unlike other vendors, Rackspace associates know what they are doing.

Goods:

1. High Reputation IPs;
2. Very Reliable;
3. Not blocked in any counties (Google Apps blocked in Mainland China);
4. Amazing Spam filtering. We were using Tencent Bizmail, one noticeable change when switched to Rackspace is the dramatic decrease in spams;
5. No more “550 IP frequency limited”.

Bads:

1. Slow development: DKIM support;
2. Slow blacklist removal;
3. I still don’t know if I can send emails using alias domains.

Conclusion:

Rackspace is a “almost perfect” email hosting solution provider.

PS. DKIM support is finally completed, contact support to manually enable.