[ale] Sendmail latency

[Jim Popovitch]

--- Ryan Fish <FishR at bellsouth.net> wrote:
> 
> - The actual IP for this app server is .221 so I have no idea why it is
> coming back as .0

This could be a red-flag.  I would check the dns servers listed in
/etc/resolv.conf to see if they return an incorrect IP address for that host. 
Just as a check, verify that from each server you should get accurate
information for these four commands:
 
   # host <server1>
   # host 192.168.3.221
   # host <server2>
   # host <IP_Addr_2nd_Machine> 

> 
> 
> Everything worked fine prior to rebooting the app servers around 5A on
> 14JAN.  Afterwards all of this started...
>
> 
> I see very few errors in the maillog.  Here is a sample of some:
> 
> Jan 24 23:24:33 mailserver sendmail[5617]: j0LHsHCx010652:
> to=<user at outsidedomain.com>, delay=3+10:30:11, xdelay=00:00:00,
> mailer=esmtp, pri=7327408, relay=mail.outsidedomain.com. [38.113.1.50],
> dsn=4.3.0, stat=Deferred: 451-host lookup did not complete

A log of these are indicative of a DNS problem.  A few here and there are
pretty normal.

> 
> Jan 24 23:27:56 mcmail02 sendmail[5617]: j0LFWuTF026717:
> to=<user at otherdomain.com>, delay=3+12:54:55, xdelay=00:00:15, mailer=esmtp,
> pri=7502182, relay=otherdomain.com. [38.161.171.51], dsn=4.0.0,
> stat=Deferred: Connection refused by otherdomain.com
> 

A few of these during "rush hour" is all too common.  Repeated refusals need to
be investigated.  Just curious, are those valid domains or have you changed
them to otherdomain.com and outsidedomain.com? 

> 
> - I don't know how to obtain the 'stat' output of connections in
> /var/log/maillog...

I was just referring to the "stat=Deferred" statements you showed above.

On my systems, I see slow email delivery under 2 different situations.  The
first being high load average, thus causing sendmail to throttle itself. 
Secondly, when DNS has latency/resolution issues.  The trick to the second is
to run a caching DNS server on the mailserver and have /etc/resolv.conf use
127.0.0.1.  It is possible that your issues are related to DNS resolution.

Btw, "Connection refused by otherserver.com" type messages can be a result of
their mailserver not liking yours.  Make sure that your mailserver has a valid
PTR (reverse DNS) entry.  Also use a site like openrbl.org to verify the
'cleanliness' of the IP address of your mailserver.

-Jim P.