[Mimedefang] Using relay_is_blacklisted() or Sendmail dnsbl feature ?

Ole Holm Nielsen Ole.H.Nielsen at fysik.dtu.dk
Tue Jul 1 10:47:01 EDT 2003

We're having a performance problem with Sendmail 8.12.8
running on a Red Hat Enterprise Linux ES 2.1 server.

Using Sendmail's DNS-blacklist feature,
    FEATURE(dnsbl,`bl.spamcop.net', ...
I'm invariably seeing delays of 30-90 seconds when delivering
messages, even when I use only a local dnsbl-server with
sub-second response.  The server is not loaded at all
(it's a 2.0 GHz Intel Xeon server).  I have no such problems
with a Redhat 9 server using the same dnsbl-servers, so I
wonder if anyone out there knows of Sendmail 8.12 problems on
Redhat ES2.1 (or the similar Redhat 7.2) ?

Anyway, I wanted to try to replace Sendmail's dnsbl lookups
with the corresponding mimedefang-filter function
relay_is_blacklisted().  However, I don't know where
it's appropriate to insert calls to relay_is_blacklisted()
in the default mimedefang-filter script.

Question: Can anyone explain the details of proper usage of
relay_is_blacklisted(), and perhaps shed light on Sendmail's
dnsbl lookup problems ?

Ole Holm Nielsen
Department of Physics
Technical University of Denmark

More information about the MIMEDefang mailing list