The code itself works, mails get properly sent. The problem is on the other side - I need to send mails to a pretty aged interface that parses them and over which I have no control. It doesn't accept and parse anything that isn't plain text, so mails with Content-Type: multipart/mixed and encoded contents get rejected.
I solved the problem temporarily by using smtplib directly. As soon as I manually send messages with body simply consisting of: /n Some simple text here. /n/n everything works fine, they get parsed properly on the other end. Is there is any way to trick web2py's Mail class into sending emails with absolutely no body encoding? I looked at the gluon/tools.py in the mean time and it seems that what I'm looking for is impossible to achieve trough web2py's Mail class. Unless I'm mistaken... Anyway, Thanks for looking into this!