Allowing only domain users to send emails to group emails

Hello,

I"m new to postfix.

Is it possible to filter mail sent to internal group
email address so that *only* domain users can send
to the group email address?

For example. quality@ex... is the internal group
address for users a,b,c of example.com

I want only users from example.com send emails to
quality@ex... and not from any other domain.

This is to restrict spam and other non-domain users
from misusing the group email address.

How do i filter senders to this email and discard
mails from other domains?

Please excuse me if this is the not the correct list
and pointers to post it to the appropriate list would
be helpful.

Thanks,
Josh



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