[CentOS] Probelm with some smtp MTAs

[Les Mikesell]

James B. Byrne wrote:
> I am getting large numbers of these types of messages in my maillog files:
> 
> somehost.hotmail.com [65.54.246.97] did not issue MAIL/EXPN/VRFY/ETRN
> during connection to MTA
> 
> on both of our external machines beginning on the same date.  These hosts
> sit on different netblocks and on both machines the sendmail.cf files date
> from  Jan 09, 2007.
> 
> The last successfull connection from any hotmail acocunt was on Jan 15 at
> 13:17:29.  The first failure was recorded on Jan 15 at 18:36:46.
> Does anybody have any idea what is going on?  We are now getting reports
> that hotmail users are getting a delayed transmission warning and then a
> failure message.  Is this a sender's issue or our local configuration
> issue?
> 
> ANY help regarding this matter would be most appreciated. If you feel that
> sendmail related items should not be discussed on the list then please
> contact me privately.

It sounds like they are dropping the connection before getting very far 
in the conversation.  This can be caused by either end, but the likely 
place to check is any spam-screening operations you might be doing that 
could impose a delay on your initial greeting, like having greet-pause 
set or using one of the network blackhole services that could be taking 
a long time to validate this address.   Other places that can add delay 
are your reverse DNS lookup and an ident query on the socket.  The 
latter can cause a long timeout if it hits a firewall that silently 
discards it without an ICMP 'denied' response.

-- 
   Les Mikesell
    lesmikesell at gmail.com