Reverse DNS and mail

Len Conrad LConrad at
Wed Jan 7 19:01:40 UTC 2004

>I am thinking about (finally) setting up reverse DNS.  Occassionally someone
>reports the error " (reason: 501 Domain must resolve)" when trying to send
>mail to us.  I simply want our mail servers, which serves mail for several
>domains, to work properly with reverse DNS.
>How does one setup reverse dns when a server supports multiple (virtual)

Set up as below (Len's "best practices") and I doubt you will ever have any 
trouble getting your mail delivered (and if you do, I'd like to know):


1. the IP A.B.C.D of the MTA has a PTR hostname (eg: label.domain.tld) ...  PTR label.domain.tld.

2. ... which hostname has an A  record whose rdata field matches the MTA's 
IP (and preferably an MX).

label.domain.tld. A A.B.C.D.
label.domain.tld. MX 10 whatever

In the MTA's SMTP settings:

3. The MTA's HELO hostname is the same as the PTR hostname:

EHLO label.domain.tld

4. the MTA's SMTP-greeting hostname is the same as the PTR hostname:

220 label.domain.tld

Note that the (virtual) envelope/recipient domains of the traffic allowed 
by the MTA's policies are not a consideration in the above settings (the 
ESD/ERD don't have to match the above label.domain.tld).


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