serious email woes

[michaellunsford]

I have two different domains. One has email disabled, and the mx records redirected to another server -- which works fine.

part two is the problem. The second domain has email hosted locally, and one user is forwarding their email to the server with the MX redirect.

Problem: The user gets their email, but if the sender happens to be from the second domain, they get a bounce from the server:

Hi. This is the qmail-send program at server.example.com
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

Again, the intended receiver gets the e-mail, but the sender gets a bounce.

How do I fix this?