Right now I can't investigate if the problem is on our side or not, but can you open a ticket with EPiServer Developer Support and they will look into it first thing Monday. Also just to be on the safe side, enable EPiServer logging and see if you can find any errors regarding EPiMail there.
Since yesterday morning (may 27) we are experiencing problems sending mail using EPiServer Mail.
Everything seems ok on our side and we do not get any warnings on submit, but we and our customers doesn't receive any mails.
After troubleshooting it for a while I now suspect that the problem is on EPiServers side and since I have trouble reaching them or our partner on a Saturday I would like to know if any of you are experiencing the same problem?