Block auth senders using other domains

[Dominic Raferd]

My domains are listed in virtual_alias_domains and my legit 
senders/recipients in virtual_alias_maps.

I recently discovered the 'reject_unlisted_sender' option which 
successfully prevents (auth) senders from sending from an unknown 
name@mydomain. For instance f...@timedicer.co.uk is blocked as a sender. 
This is much simpler than my previous approach to this problem.

But it doesn't stop them sending from a different domain that is not 
listed in my virtual_alias_domains, such as f...@gmail.com. Currently I 
stop this with my own check_sender_access file (in an smtpd restriction 
list applied only to auth emails) that DUNNOs my domains and then 
REJECTs all others.

I feel there is (or ought to be) a way of achieving this that does not 
require creating a bespoke file/entry. I see 
'reject_unknown_sender_domain' but it does not match my use case, and I 
cannot use 'reject_sender_login_mismatch' because some users need to be 
able to send from >1 name (all @mydomain) but using 1 login. I think I 
want 'reject_unlisted_sender_domain' (which does not exist).

Am I missing something?