Sometimes when Exchange Server is put in place at the start of a migration to Exchange, the admin may attempt to use POP3 with Exchange to retrieve mail from an ISP's POP account for storage in Exchange. It is possible to make Exchange do this with third-party add-ons, but in general this is not a good idea. This is true for either Exchange 5.5 or Exchange 2000.
One of the common misconceptions about POP3 is the belief that it is both a client/server and a server/server protocol. It's a client/server protocol only -- it's designed to work between a client and a server, and is not designed to allow communication between two servers.
Here are the major reasons why you should avoid using POP to obtain Exchange mail whenever possible.
- The SMTP delivery envelope is lost during a POP conversation. When a client connects to a POP mailbox and obtains mail, the SMTP delivery envelope is removed and destroyed. This envelope contains critical delivery information, and also contains details about how the messages are composed. HTML attachments, for instance, or any attachments at all will often come through shredded -- if they even get delivered correctly. If you have multiple users sharing the same POP box -- an even bigger no-no -- it is next to impossible to properly distribute the mail from that box once the mail has been obtained.
- POP uses clear-text passwords. Most POP mailboxes support only cleartext password authentication. If you are trying to enforce any degree of security at all in your organization, you will understand that transmitting passwords in cleartext is inherently dangerous.
Take the time to have your email forwarded properly and to have MX and DNS entries configured correctly for your Exchange server. Don't waste time with kludges that can only do more harm than good.
Serdar Yegulalp is the editor of the Windows 2000 Power Users Newsletter.