Exchange Server 5.5 Time out errors while waiting for message body

NT4.0 spk6a , Echange Server 5.5 spk4 . The exhange server is timing out when receiving email via SMTP  Here is the event log
EVENT ID: 4051 A timeout occurred while trying to receive mail from c-69-141-227-107.hsd1.nj.comcast.net and while waiting for the  message body.  This happens from other domains not just comcast . Intra office  email works.

Tests performed to try to isolate network, router or Server errors

1. I blocked all SMTP connections to the server via the firewall , and only allowed SMTP/pop3  connection from one IP address, from this ip address I attempted to send and receive email to the server and received the same error 3 out of 5  tries , if an attachment  is present in the email (not a very big one either 10K pdf) it times out all the time. All out going email works fine..just erros on incoming

2. There are no hardware or network errors in the event logs and I never lose connection when I am remotely working on the server.  I did a ping test across the lan and no packets are being dropped

3. I captured some packets and no Lan errors detected ..

Please help