Seems to me that no one has answered the original poster's (jabrocuk) question (which is the same as mine).
One poster (DavidR) asked if the email account used SSL even though the original posting clearly indicated "No."
The question for the OP was still valid even if the error mentions SSL = No, if the account required SSL (via avast redirection) then it would fail to connect.
Another part of the eror message indicates that the attempt to connect was using SSL, so one way or another we need to know if it is an SSL requirement or not:
Server error: 421 Cannot establish SSL with SMTP server xx.xxx.xxx.xx:465,
That would then give us another clue where to look - Unfortunately the OP never responded to any of the questions.
Currently I believe there is a problem with the Outlook Plug-in, not working with that build (it is fixed in the current beta testing (RC build), so the Mail Shield is effectively taking over that task.
Now if yours is exactly the same as the OP, if your account doesn't require SSL, then ensure the Mail Shield, Expert Settings, SSL Accounts, account with problem, it should be set with Protocol=SMTP, Port=25 and Encryption=None, see image.