I agree with the answer, the login is the correct email address.
A dotted version is completely different and may exist (another person)-(the dot is recognised)
I usually register both undotted and dotted versions in my own name to avoid confusion, one is just a spare but prevents a similar email being created by someone with the same name which can be a nightmare, and result in getting other peoples mail.
The settings should match the username used for the email login, but I would advise the virgin contact email to be different, better for recovery to have a recovery email/contact (non-virign) email listed.
In google gmail the dot is not recognised so the two address would be the same. (this is the only exception)
There have been issues recently with email not been received by virgin email.
Re: Email forwarding not working from another doma... - Virgin Media Community - 4998000