@Safs-3080
If you remove an email address policy(@domain123.com) from a mailbox, the related proxy email address(@domain123.com) still exist on this mailbox, this email address will not be removed.
From Exchange side, after enabling admin audit log, you can use it to check if admin add/delete proxy email address for a mailbox:
You can also check whether admin create/delete a new email address policy:
You can click on this one to check email address policy applied on which mailbox:
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