>>> and various config for outoing email smtp
>>> e.g. smtp.three.co.uk - smtp-mmb.three.co.uk,
>>> with different server port numbers 25 - 587
>>> etc. Still not able to send.
Outgoing server address should be SMTP-MBB.THREE.CO.UK (note MBB, not MMB) although, if I remember correctly, it took an absolute age for the sent emails to arrive.
If your own ISP supports SMTP Authentication, that is a better solution. If it does, you enter your Username/Password in the same way as when accessing an incoming POP3 or IMAP server and can then use it with any internet connection.
P.S. I've just sent myself a test message via my "3" dongle using the server SMTP-MBB.THREE.CO.UK and it went through in a couple of minutes, so perhaps the service was having an "off-day" the last time I used their email system.