reverse DNS (was: Provo Internet options)

Wade Preston Shearer lists at wadeshearer.com
Tue Nov 28 13:48:41 MST 2006


> FYI - AOL will not work without reverse DNS

Speaking of this…

AOL will not accept email from my server because of this. I don't  
care to ever send an email to an AOL user, but I have a few with  
accounts on my server, such as my father, who occasionally do. What  
is the group's general feeling about this? Keep my heels dug in as a  
purist?

[1] From http://en.wikipedia.org/wiki/Reverse_DNS_lookup:
"Reverse DNS was designed to be primarily a tool for network  
troubleshooting. However, it is sometimes used as a poor defence  
against spam. When an Internet mail server receives incoming mail  
from an external machine, it may check that the reverse DNS record  
for the IP address of the originating server matches up with name by  
which the originating server identifies itself during the SMTP  
greeting. […] This is not a good defence against spam for several  
reasons. One is that a machine can have more than one IP address and  
any number of domain names, and the mapping between IP addresses and  
domain names is essentially arbitrary. Another, perhaps more  
relevant, reason is that a single client or server machine can  
legitimately send mail that is "from" an address in a domain  
different from that of the machine. There is no expected relationship  
between the domain name of a mail client or server and the domain  
names of the email addresses whose mail it originates or accepts.  
This is intentional, and essential to allow the outsourcing of a  
company's email handling. A third reason is that due to NATs the  
source IP address seen by the server may be different than the source  
IP address used by the client."
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