Mobileme on ipad won't send mail

I've got a Mobileme account set up on my ipad (i set it up directly on the ipad, not through syncing with itunes). It's been receiving emails fine, but I seem to have trouble sending email out.

I tried sending emails FROM my Mobileme account TO another account of mine (in this case, a gmail account).

The emails seem to go out - i get the sent mail sound, and the emails appear in the "sent" folder, but the mail never arrives!

Anyone else have this issue? Thanks!