I am having exactly the same trouble.
Email through another network, (say, my home or work wifi) works correctly and I can send and receive messages.
However email when using the T-Mobile wireless network does not connect.
This is obviously not an activation issue. My account is not deactivated if I can send and receive messages using another network, so using the pin activation page is not the appropriate fix for this problem.
According to t mobile support, there is a problem with the verizon protocol server, and it does not work with the t mobile network. T mobile engineers are working with verizon to resolve. Verizon insists that there is no problem at all and everything is fine and working well.