The webmail issue is not one I have read of before so will leave that to one side for the moment.
It would be helpful to see what, if any, error code is returned by the SMTP server in this situation. Open a Command Shell or Terminal window and enter the following where username:password is replaced with your email address and password, i.e. richard.branson@virginmedia.com:Y54kpX5g:
curl -v smtps://smtp.virginmedia.com -u username:password
Do not post the resulting output here but instead review it for possible reported causes and then post just the redacted part here or the VM error code.