DNN Just installed 5+ using the web installer from MS. Was stuck on the mail settings and I use a gmail smtp.
So the correct way to get around it was to enter smtp.gmail.com:587 http://mail.google.com/support/bin/answer.py?hl=en&answer=13287
I tried no port with SSL checked and appended :465 with SSL checked so :587 with SSL checked and the whole email account address.
That at least gets me on to the next steps.