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Event ID: 20031 Source: SmtpEvt

Source
Level
Description
An unknown SMTP command.

For more information, see Help and Support Center at http://go.microsoft.com/fwlink/events.asp.
Comments
 
I disabled the smtp filter on the ISA server, and it seems to be allright now.
As per Microsoft: "This issue may occur if a firewall blocks the binary large object (BLOB) data following the Microsoft Exchange Server XEXCH50 command". See ME818222 for a workaround.

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