Exchange attachments delay error

On all emails with attachments I receive this error message no matter what the size is. We can send attachments internally on the intranet but all web or internet sends come back with this delay message. I read an article about Cisco Pix being the problem. I do have a cisco pix but the gateway for the exchange server is not routed through this gateway.

This is an automatically generated Delivery Status Notification.

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

Delivery to the following recipients has been delayed.

schd1it@cox.net

any ideas about what is causing this?