Every so often my users (system wide) cannot open attachments to their e-mails in MS Outlook 98. The error says the attachment can't be opened or opens up M/S Explorer instead. We are running Exchange Server 5.5 (Build 2650.24:Service Pack 3) on a dedicated NT 4.0 (Build 1381: Service Pack 6) server that also serves as the PDC. If you reboot the mail server, the problem resolves itself, only to reappear later. This has occurred 3 times since May 1. Thanks for your assistance.