Under certain circumstances, e-mail clients attached to Exchange 5.5 or Exchange 2000 may start receiving multiple copies of inbound Internet e-mails. There are several common reasons why this may happen, each with its own symptoms and solutions. This tip presents the three most common, presented in descending order of likelihood:
- If the clients receiving the duplicate mails are using Outlook, chances are it has been configured with both the MAPI mail client and the Internet mail client -- both of which are polling the same Exchange mailbox. In circumstances like these, either remove one of the clients entirely (depending on how your organization is set up), have it point somewhere else, or have it not poll that particular address during a send/receive cycle.
- Exchange servers that are attached to Cisco PIX firewall appliances may be running into a problem with Mailguard, the firewall's SMTP protocol filtering feature. Mailguard blocks Extended SMTP commands and allows only basic SMTP, a feature that is designed to protect poorly designed mail servers from being hacked. If your Exchange 5.5 or 2000 installation has the most recent set of updates, it probably doesn't need Mailguard, so you can turn it off. Barring that, it is also possible to eliminate the problem by upgrading to the latest version of PIX, which corrects Cisco bug # CSCds90792.
- Another, more exotic variation of the problem pops up if a user's mailbox is located on an Exchange Server 5.5 computer, and is also a member of a distribution list on a computer running Microsoft Exchange 2000 Server. The Exchange 5.5 account may receive duplicates of a message sent to the distribution list with the user himself CC'd. There is very little that can be done about this, barring merging the distribution list and the user's account on the same machine.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter.