Ok, I managed to get it working :)

Seemed that Gmail was blocking access to SimpleMail (got a notification mail from Google for illegal access to my account).

For whoever faces the same problem in the future, after you have enabled imap on the gmail settings head on HERE and enable acceess fom less secure applications. OWB didn't do the trick and I had to resort on Mozilla/PC to enable that option. After you have successfully enabled it you will receive a confirmation mail from Google. Now go to SimpleMail account settings and fill in the blanks.

Also, wasn't suppposed that SimpleMail 1.1 would display HTML and unicode (i.e. Greek letters)? Because both of them don't seem to work. HTML mails display just a url link (i.e. from Nike.com) and when I receive a mail to Greek I only get "____" (without the quotation marks).