Hi aldogreat,
Just to save me re-typing out the suggestions, ... have a look at this recent thread (see below) which should hopefully start you off in the right direction. First thing to do is check what error code is given for the reason why you can't send. See 用心棒 first reply ....
https://community.virginmedia.com/virgin/board/message?board.id=email&message.id=210549#M210549
Also have you checked your IP address to see if it's listed in the Spamhaus blacklists? ((Ignore the fact that you'll be on the PBL list, as all "normal" users are on this one)).
Go here ..... https://www.spamhaus.org/lookup/
...and enter your IP address (find it by typing "What's my IP" into a Google search).
Good luck 👍
