[ On Wednesday, January 8, 2003 at 10:07:47 (-0000), Mark Douglas wrote: ]
> Subject: Re: [Exim] DNSBL Question/Alert
>
> > the (Osirusoft) DNS blocking list check began timing out
>
> Yesterday morning I was caught by this. Most SMTP connections were
> timing out and we eventually traced it to the Osirusoft lookup
> hanging. I removed that lookup and things seem normal.
If most of your SMTP client connections were timing out when a DNSBL was
unavailable then either your SMTP client are _very_ poor quality and
non-standard implementations, or your DNS resolver is waiting far too
long for responses.
Clients are supposed to wait at least FIVE minutes for the intitial 220
message, and also 5 minutes for the response to the MAIL and each RCPT
command too.
If your Exim was delaying the initial 220 response, or its response to
MAIL and RCPT commands for over five minutes, then your DNS resolver is
seriously broken.
FYI none of the systems I manage had any problem handling the
osirusoft.com outage, though they did exhibit more than the average
number of simultaneous connections for the duration of the outage (which
is only to be expected when each connection lasts at least a full minute
or two).
--
Greg A. Woods
+1 416 218-0098; <g.a.woods@???>; <woods@???>
Planix, Inc. <woods@???>; VE3TCP; Secrets of the Weird <woods@???>
