SBL blocklist query trouble

[Roy Bixler <rcb@ucp.uchicago.edu>]

I'm wondering if anyone else has had a problem with trying to query
the SBL (sbl.spamhaus.org) blocklist via the SMTP server.  I first saw
this trouble with a Debian Linux box running the 2.99.55 prepackaged
SSL version of ZMailer.  Inbound SMTP connexions just hang and the
smtpserver process consumes 99% of the CPU.  With sufficient number of
these stuck SMTP connexions, the system gets very slow.

At first, I thought the problem was with the libc version on that
system and, since it wasn't an important machine to be receiving mail,
I simply disabled ZMailer for a while.  Then, on a NetBSD 1.6.1 system
running some CVS version of ZMailer (it advertises 2.99.56-pre3
version and was built about a year ago), I saw the same problem occur
just after I added SBL to the blocklists I use.  When I removed SBL,
the problem went away.  After I did the same on the Debian system, the
problem went away there too.

The funny thing is, that if I do the queries manually using the 'host'
command, they work normally.  Does anyone else see the "stuck inbound
SMTP connexions problem" when using the SBL?  Any ideas?  Of course
this may be an SBL DNS setup problem, but I'm hesitant to bug them
unless I'm sure that it's a problem with their DNS setup.

Regards,

-- 
Roy Bixler <rcb@ucp.uchicago.edu>
The University of Chicago Press
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