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

[Jonathan Dill]

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 [206.46.230.37] and not 
the IN MX address relay.verizon.net [206.46.232.11].

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

http://www.python.org/cgi-bin/faqw-mm.py

Jonathan