This article was previously published under Q312213
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You may receive the following Event ID 240 error message:
SMTP command exceeded its allowed length
Additionally, in Microsoft Exchange, an error that resembles the following may be logged in the Simple Mail Transfer Protocol (SMTP) log:
421 5.5.2 Syntax error (command line too long)
This issue may occur if a Microsoft Internet Security and Acceleration (ISA) Server-based computer has an SMTP Application Filter that is turned on. The default SMTP filter value for a NOOP SMTP command is 6 bytes.Exchange Server 5.0 sends a NOOP SMTP command that is longer than 6 bytes when it sends SMTP mail.
To resolve this issue, increase the SMTP filter value for the NOOP command in the ISA Server SMTP application filter to 1,024.
The NOOP command is one of seven minimum SMTP commands that have to be allowed for the SMTP process. This command does not affect any parameters or previously entered commands. The command specifies no action other than that the receiver send an OK reply. This command does not affect the reverse-path buffer, the forward-path buffer, or the mail data buffer and may be issued at any time. If a parameter string is specified, servers should ignore it.
The syntax of the NOOP command is as follows:
"NOOP" [ SP String ] CRLF
Note There is no Requests for Comments (RFC) that specifies the default size of the NOOP command. The command is 6 bytes by default (N + O + O + P + CR + LF).
For more information, see RFC 821, "Simple Mail Transfer Protocol" and RFC 2821, "Simple Mail Transfer Protocol." To see these RFCs, visit the following Web site: