I have sendmail configured as a smart relay to an Exchange server. The mail relay is working fine and only has to worry about relaying mail from a single application address to the end users. The problem is that those users are in separate domains and neither wants to see these application mails as coming from the other domain.

I'm trying to find out if it would be possible to rewrite the sender address based on the recipient address. So if a message is sent from application@domainA.com to someuser@domainB.com, the "From" address would show as application@domainB.com.

Has anyone done something like this before? My research so far has shown that a milter like MIMEdefang could possibly accomplish this, but I'm not 100% sure if that's the right track or not.

I'm open to suggestions or examples of how I might achieve this.

I ended up not using Sendmail for this after all. Instead I installed Postfix using a Slackbuild from Slackbuilds.org and enabled it to relay to my Exchange server.

The first step was adding an additional transport in /etc/postfix/master.cf that looked like:
Then I added this line to /etc/postfix/main.cf:
Next I added this to /etc/postfix/transport:
That line tells it to use my new transport for any mail addressed to someone @domainB.com.

Created and edited /etc/postfix/generic_smtp2 to look like:
Finally ran and restarted postfix.

Now any messages from domainA.com to users at domainA.com are unaffected. But if the email is addressed to someone at domainB.com, then the sender address is rewritten to look like it's from domainB.com as well.

I had to actually create a user account in Exchange for the address after it gets rewritten (such as application@domainB.com) so that if a user replies, it actually goes to a mailbox.