%virginmedia.com@gtempaccount.com

Where are you seeing this unexpected email address appear?

You state you are now a VM broadband customer but in some of your previous posts some time ago you were trying to deal with a mailbox when you were no longer a VM customer.

Is the mailbox in question your primary VM email address (the one you use to see bills, your contract etc.)? If not, have you logged into the primary account for 'My Virgin Media' and checked that the maibox you are trying to add to the phone is still listed under your broadband account?

There are multiple changes going on with VM email at present including changes for security and VM deleting orphaned mailboxes.