As per ravenstar's prompt I have inspected your SMTP logs and note the VM304 error, dated for the 7th.
Emails sent from a BT IP were successful whilst those sent from your VM IP were not. At this point I noticed you seem to have made some recent changes to your account which have resulted in your blueyonder email being isolated on an account with no active services. This will need to be sorted out before I can escalate the VM304 to I.T. although it's highly likely that this is the cause of the error anyway.
I shall send you a PM (purple envelope icon, top right of page) in a moment so that we can discuss how best to get this issue resolved.