ExchSrvr 5.5 / OL 98

We are running Exchange Server 5.5 on NT Server 4.0 Sp6a. We only have this one exchange server. All workstations ( NT, 9X, Thin clients on Terminal server ) are using outlook 98. My problem is that some users’ inbox do not update. Users within our company will send each other a message and they don’t get it until they exit from outlook and then start outlook again. Sometimes pressing the send/receive button will work. I have ran the defrag on the public and private database thinking that mightsolve but made no difference. Does not happen to all users. Any and all help will be greatly appreciated.

Mike