[CentOS] slow sendmail going out

Wed Apr 27 16:21:39 UTC 2011
Les Mikesell <lesmikesell at gmail.com>

On 4/27/2011 11:03 AM, Jerry Geis wrote:
> I am trying to find a way to "speed" up sendmail going out of my box.
> I am setting SMART_HOST. Dont get me wrong email does go out it just takes
> like 3-4 minutes to get there.
> When I do "mail xxxx at y.com" and send it the /var/log/maillog file shows
> the connection and shows the relay as []. Then it just SITS
> there for a long time.
> Then it picks up the mail and delivers it. No errors are show, no
> timeouts etc...
> My box does not have an MX record as  I am behind the firewall
> (192.168.1.X).
> I have set the /etc/sysconfig/sendmail QUEUE=1m but that does not seem
> to help either.
> There is nothing else happening on my box so that is not slowing
> anything down.
> I've done some google'ing, some playing and nothing has helped. I tried
> adding the service.switch
> to sendmail.mc, I tried temporarily taking out dns from nsswitch.conf -
> and nothing seemed to help.
> How can I get emails exiting my box faster.

Sendmail normally does a reverse DNS lookup (number to name) for the 
connecting IP and an IDENT query on the socket.  If you've configured a 
firewall to drop these from the receiving mailer, you'll wait for a 
timeout to happen.  Rejecting with an ICMP-denied makes it fast, since 
it tells the other end not to wait.  Note that these will come to the 
public side of your NAT router.  The remote will also be checking that 
it can resolve the domain in your From: header and probably some other 

   Les Mikesell
    lesmikesell at gmail.com