[Exim] me again

Firstly, happy new year to everyone.

I have 2 domains foo.com & bar.com.
The foo domain is obsolete (other than a few critical addresses)

What I would like to do is:

When a mail comes in for, say, user@???, I would like
to autoreply to the sender informing them that the account is disabled
and that the mail must be sent to user1@???.

I also need to leave the critical addresses alone.

so user@??? must autoreply BUT critical@??? must NOT.

any ideas would be appreciated.

Thank you all.

Regards,
Tom Kinghorn