Not receiving all emails from outside our organization.

[tdoma]

I need help. We are currently not receiving all emails incoming to our organization. Does anyone how I can go about troublshooting this issue. For example I sent 10 messages to my doma@care.org account, but only received 6. I am not getting NDRs that could help point to something. If it helps our DNS records are hosted by our ISP. We have an internal DNS for a W2K AD environment. The messaging servers are a mix of E2K3 and Exchange 5.5. The Exchange 5.5 is a bridgehead server which is akso running X-400 connectors to some of our international offices. We are a Microsoft/Cisco (routers, fix, vpn concetrator and switches) environment.
I hope someone can help with this.

 

[ndwalker]

Do you have any AV software integrated with Exchange by any chance? I installed McAfee GroupShield 6 onto my Exhcange box and had to roll back to 5.2 as mails were just disappearing.