[Mimedefang] Autoresponse to old domain

[Shawn Button]

I posted this on the sendmail group with no response...I apologize since
this is probably off-topic but I am not sure where else to post...

Sendmail 8.12.8 (patched) latest mimedefang and spam assassin...

We recently changed our company and thus e-mail domain name. Our server
is now set up to receive mail for both domains (ie old.domain.com and
new.domain.com). Is there a way to set up an auto responder that
whenever a mail is sent to old.domain.com it is delivered but a response
is sent to the sender stating something like, "thanks for contacting
old.domain.com. Your message has been delivered but please note our new
e-mail domain is new.domain.com."

Any ideas?

Thank you kindly...