[AugustH]

I suspect it's a bug in the iPad Wi-Fi driver. Sitting here on my net I can physically see the DSL router (hooked to my Airport Extreme), and when I pull up Mail on the iPad it says "checking for mail" and the router is showing no activity at all going in or out. Then after a long long delay (greater than 30 seconds!) there's some activity and Mail updates. This sounds like a DNS issue where the iPad isn't resolving the server's IP address. There's no way to set the DNS server on the iPad that I can see, so it must be getting it from the router (if set).

I am interested in seeing what your packet analyzer sees, especially for resolving the server names.