They do if they were in bt group prior to Openreach, but they may not know it.
If its a shared system (e.g. MS Exchange or similar) then primary and secondary aliases are very easy. One system I managed some staff had 6 incoming email aliases due to the number of mergers and acquisitions. Sending address is always up to the mail system admin, but can be different per mailbox. Other systems can also do this, quite easily.
21 years of broadband connectivity since 1999 trial - Live BQM