[Mailman-Users] "disable_dns_lookups = yes" is a very bad idea

Jonathan Dill jonathan at nerds.net
Sat Feb 18 05:06:43 CET 2006

Speaking ripe from experience, the Mailman FAQ suggests turning on 
"disable_dns_lookups = yes" to improve the performance of Postfix with 
Mailman, which kind of makes sense.  BUT in Postfix, this disables all 
MX lookups.  So, unless you are going indirectly through a relay that is 
going to handle MX lookups for you, Postfix will begin trying to deliver 
e-mail to stupid addresses.

The symptom was that deferred messages were piling up with "Connection 
refused" errors, at first I thought I was getting blacklisted or 
something.  Finally, I noticed that e-mail to verizon.net for example 
was trying to go to the IN A address verizon.net [] and not 
the IN MX address relay.verizon.net [].

I added a note to the Mailman FAQ on this page:



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