Why doesn't SMTP generate a sign-on response?

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Question

When I use telnet to connect to my SMTP server on port 25, I don’t get a sign-on response – for example:

200 mail.company.com WindowsNT SMTP Server v3.02.13 ready at Mon, 12 May 1997 09:18:52 +0100

Answer

This can occur if ‘SMTPResolveHostname’ is enabled.

SMTP uses gethostbyaddr to do a reverse lookup on the client IP address.
It seems that this can hang if there is no entry in the HOSTS file and
there is no DNS available (MS Bug).

The workaround is to include an entry for the client IP address in the
HOSTS file.

The HOSTS file is in the NT system32 directory in the sub-directory

driversetc

This is not a problem in version 4 or later of GMS Mail.

Keywords:SMTP hung startup delay signon gethostbyaddr

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