Hi Warblers01,
Thanks for your post and apologies to hear you're still having an issue with this despite the help from 用心棒 so far.
The error code also code mean that your email settings contain an invalid combination of username and password to authenticate your outgoing emails. Your username needs to be your full VM email address, so 'Forum.Team@virginmedia.com' (or @ntlworld.com / @blueyonder etc) rather than just 'Forum/Team' for example.
If this is correct already, please remove the email account completely from the client and add back with the new credentials to see if this helps.
Pop back and let us know.
Thanks,