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Cisco MailGuard and Exchange 2000 - Confusion

I will be implementing an Exchange 2000 server in a new environment.
Right now, mailguard is enabled on the Cisco PIX.  

Does anyone know what this will do if the only mail received on this connector is outside email?
All other instances I have seen have disabled the mailguard feature.

Should it be disabled or enabled????

From a Microsoft article:
It says that there may be issues if mailguard is disabled but then goes on to mention only clients that need to authenticate with the ESMTP server.

This is from a Cisco article:
Note: If you have an ESMTP server behind the PIX, you may need to turn off the Mailguard feature to allow mail to flow properly. Also, doing Telnet to port 25 may not work with the fixup protocol smtp command, especially with a Telnet client that does character mode.

From the following website:

1 Solution
Bottom line - if you want your Exchange server to work, disable the fixup (old term "mailguard")
  no fixup protocol smtp 25

If you only receive email from specific servers, then you can control that with the access-lists and not worry about the fixup.

Notice that Microsoft article only tells you that the resolution is to disable the mailguard feature, it does not tell you that you can disable those features in the Exchange server (don't ask me how, I'm not an Exchange guru, but I'll bet it can be done)

The next version of PIX OS may address this issue and allow the ESMTP commands within the fixup inspection..

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