Delayed Mail Delivery

[Modeverything]

I am having a problem with mail delivery in my Exchange 2000 organization.

My users reported a problem to me saying that sometimes when they send an email, it can take several hours for the receipient to receive it. It has been confirmed that this happens whether or not the message originated internally or externally.

I have traced some of these messages and it turns out that these messages are being delivered to the clients in the proper amount of time, it just seems as though the Exchange server is not notifying client workstations of new mail. I then verified this with a coworker of mine, when he initiated activity on the Exchange server by accessing one of his emails and then three more emails were suddenly delivered to his inbox with times stamped spanning over 45 minutes.

This doesn't happen often, and I have only found 5 people that it has happened to, out of 500. These users located within the same Administrative and Routing Groups. I am running my Active Directory in Native Mode and my Exchange Organization in Mixed Mode, but I do not have any Exchange 5.5 servers however, we have just been too afraid to click that Native Mode button with problems going on.

Thanks for any help that may be provided.

 

[CarinaHomesIT]

I saw your post and I am fighting with the same problem with my Exchange Server. Were you able to find a resolution?

 

[Modeverything]

I did finally find the problem that was causing the delay. It turns out that the Exchange server was unable to notify the clients when new mail arrived due to a software firewall located on the clients.

The Exchange server would send a UDP packet to the client to notify it of new mail, but the firewall installed on the client was blocking UDP incoming packets. That's why when the client initiated the activity, requesting information from the server, all of the messages would be retrieved.

Hope this helps any others who may be having the same issue.