We have co-located a Windows NT Exchange 5.5 SP3 server with our ISP and we have about 14 Outlook clients running from our office. All of the Outlook clients are configured as Exchange connections, not as Internet connections.
There seem to be a lot of interruptions with getting mail as well as a delay in receiving e-mail. After I hit Send and Receive I get nothing, but when I click on the Inbox or try to send a new message, all of a sudden I receive all of the e-mails that were previously not there. Is Exchange designed to be used over a WAN or should we just move this server back into our LAN?
I wouldn't run Exchange over a WAN unless you have a private link or high-speed VPN—but that's just my opinion.
I'd bet that in this case there is a router or firewall that is not passing the RPC packets from the Exchange server to the Outlook clients as it's supposed to.
My advice would be to bring this server back in-house. Unless you have a 10Mbit/sec. connection to your ISP you'll probably see a significant performance advantage, and the reliability should increase as well.