We have 3 mail servers running Exchange Enterprise 2000 SP3 plus post roll-ups. Each mail server is an active/passive cluster running on windows server 2000. We have approximately 8000 mailboxes spread across these 3 servers. We have one large Public Distribution Group which includes nearly all the mailboxes of the corporation in nested Distribution groups with no one group containing more than 1000 recipients.
My problem is our help desk regularly sends out system downtime notifications and occasionally the delivery of that notification is delayed as much as 2 hours. This causes an issue when that email is delivered after the downtime was supposed to take place. The problem is intermittent and can not be replicated at will. The majority of these emails are delivered immediately within seconds or minutes of sending them. Any ideas as to how to resolve this or why it is happening?
One more note, we had to place an "accept mail only from these senders" restriction on this public group to prevent people from sending improper emails out to the corporation. The list of approved senders is over 100 and they are in a single group listed on the approved senders list.