[Mailman-Users] Slow delivery

vancleef at lostwells.net vancleef at lostwells.net
Fri Mar 9 04:46:56 CET 2007

The esteemed Dragon has said:
> This may just be the time needed to resolve the dns lookups for the 
> outgoing mail.
> You may want to consider using a caching dns resolver to cache the 
> sddresses for some reasonable period. Getting the resolved addresses 
> out of cache will be much faster than attempting to resolve them over 
> the network every time.
> Then again, I could be completely off here and something else is 
> causing the delay. I don't know Exim at all and sendmail only in the 
> barest manner so I cannot be much help beyond this.

Maybe this is a good time to ask just how DNS-intensive the
non-sendmail MTA's are.  I am finishing off the basics on installing
sendmail with Mailman, and am including some discussion of the need to
install a good fast-response caching DNS server to work with sendmail.

There is very little discussion in the sendmail literature about DNS,
except for an acknowledgement that sendmail uses DNS intensively if 
it's in the "hosts" line in nsswitch.conf (Solaris name).  

I have to confess that I was a bit slow on the uptake to install local
DNS on my systems.  The folks at upstream feed, whose DNS servers I was 
using, said, "you do plan to install local DNS, don't you," with a
certain pointedness.  I dawdled until I could get the 5th edition of 
Liu and Albitz "DNS and BIND" (O'Reilly, 2006), which has a chapter on
DNS and SMTP mail, and after reading through sat down to install a
caching server immediately.  

The results were just plain startling.  I wish I'd done this five
years ago.  

Since then I've installed master and slave servers for my Intranet
LAN, but I would heartly recommend having at least a plain caching
server on the box that's running the MTA.  

While all of my experience is with sendmail, I'm inclined to suspect
that the other MTA's all can stand a shot of local DNS service.
Anybody who can confirm this for Postfix, Exim, etc.?  


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