I find this tack, by BT, both interesting & confusing!
I've just transferred my Broadband to BT (although I've always had my Phone with them & my "normal" email address is registered with them & is used to access their Billing site.
However, during my Broadband Transfer process, BT set me up with an Email Address (which I hadn't asked for) &, also, decided that would be my main/only point of contact with them.
Just to make things even sillier, it was specifically stated that it would be used to provide Order progress updates - but they also stated that it would NOT be activated until AFTER the Order was completed!
Personally I have no need for this unrequested Email - they only concern would be if they sent me some important bit of Contract info that was missed!
(NB:- Hopefully, I've already re-set up that my original Email Address should be also used &, additionally I set auto-forwarding on the BT version - hence, this should catch everything!)