Hi,

I am currently running OpenBSD 4.0 as a greylisting server. We have
found that many Microsoft Mail Servers/Mail Marshal cannot get past the
greylisting. On further investigation, we found out that the MS Mail
servers send a NOOP before they start sending other SMTP commands and
spamd returns a 451 even for a NOOP causing the SMTP connection to
terminate and the connecting mail server doesn't even get greylisted,
since it hasn't even sent a "MAIL FROM" and "RCPT TO".

I've seen no mention of this in the archives, so was wondering if this
is intended and if there is a permanent fix for this. 

We've temporarily patched spamd.c, so that spamd does nothing on a NOOP
command as required by the SMTP RFC and we've seen that the MS Mail
servers get properly greylisted and subsequently whitelisted.

Sid