[exim] Mail lists, gmail servers in mx and local users issue

Our mail is hosted at gmail.

Our mail server sends our mailing lists using Exim.

Our domain is example.com

If joe@??? is on one of the mailing lists he does not receive
the mail as it is trying to deliver the mail locally rather than
sending to the gmail mailserver listed in the mx.

How can I fix this?

Thanks!
Cameron