Hi Amy,
Sorry for the delay to answer, regarding your questions those are my answers:
1. Exchange Server can get emails from any domains, the issue just happen when our own domain which is set in another email server (google apps) send emails to my distribution group.
2. I don't have any transport rule related to this distribution group or account. I saw this on EMC but if you have another way to check it out please let me know.
3. This issue started even before I installed my current anti-spam, before that I was working with Exchange Server antispam.
Is there anything else that I can do to fix it.
Thank you
Vannessa