Sendmail & Valid users

[Mike Hogsett]

I have a question regarding sendmail and this list may be able to point me
in the right direction.

What I want is to be able to verify the address in the "MAIL FROM:" during
the SMTP transaction for domains that this sendmail is responsible for.

If they are claiming to be within our domain(s) then the address in "MAIL
FROM:" should be a valid recipient.

 - Mike