I have Google Apps set up for my email server out of convenience. However, I now know they won't support IPv6 incoming mail. Not yet at least. After much searching and hmming and hawing over trying to set up an MTA on a Linux box just to pass that test, I have an answer. Disclaimer though, this is a company that likes to be paid, however all I have is a free level account, so I am posting this to be helpful. If you like their service maybe pay them.
If you visit http://rollernet.us
and sign up for a free account, they offer a Secondary MX service with full IPv6! I added it to my MX records around 40 priority, set up the forwarder to allow all ( since I didn't need spam filtering) and laughed when my test email came through minutes later. Not bad for free, and definitely simple to set up.
Let me know if this helped.