So they still haven't fixed the invalidcosdomain errors... this has been ongoing for many months.
The real issue is caused by the new ViRgin Media Registration and the Old ntl: internet database on SOME accounts, hence it doesn't affect everyone. I don't work for Virgin Media anymore, I've got a proper IT job now but this particular issue will probably not be resolved until the NEW database is created, this could be a long time.
Call the 0906 premium line if you get the cosdomain error, you WILL be refunded for the call, make sure you know your security word (usually your mother's maiden name) the Tech will add the new mail account for you manually.
I USED TO WORK FOR VIRGIN MEDIA BUT I'M
K NOW!