Glenn Anderson wrote:
I have definitely encountered what appeared to be a proxy that returned
421 and closed the connection when it encountered things it didn't like.
I wouldn't be surprise.
If I recall correctly, the proxy in question was returning 421 in
response to a MAIL FROM command with an address that didn't pass some
sort of validation it was doing, so this problem isn't limited to NOOP
commands.
Good point, let me do a quick google here....
Ok, I searched: SMTP proxy "421 5.5.2"
Very interesting! This seems this is an issue with the Microsoft
Internet Security and Acceleration (ISA) server. MS has this KB
description and resolution for it:
http://support.microsoft.com/kb/312213
It was definitely following RFC 821!! From the article:
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:
http://www.rfc-editor.org/
Go Figure!!
I hope there is some MS engineers lurking around here so they can at
least the default setting for the length in the ISA NOOP filter. :-)
--
Sincerely
Hector Santos, CTO
http://www.santronics.com
http://santronics.blogspot.com