Users who have changed domain so email address has change

Hi New here

We have been running RT for a while now, and now we have expanded and add a new domain to the organisation. So we have users who’s email address has changed, and RT no-longer recognises them.
I have manually changed their email address in the DB, but that is only allows incoming email and ticket generation.
Is there a way to allow multiply email address to an User? and if not how do I get RT to send to the new domain.

Address for main domain -
Address change to new domain -

Thanks for any help.

Are these users privileged users who should be getting email notifications of ticket workflows? Or are these normal “end users” and they’re getting replies from tickets that they already have open with their old email address?