Re: reverse DNS

From: Marko Mäkelä (
Date: 2002-09-11 13:27:35 wrote:
> Sorry to bother you all but I sent an email to Marko at three different
> addresses for some days and all were returned with the following message:

The administrators of our university network have tightened the 
configuration of the mail servers in order to better block unsolicited 

>     (reason: 550 5.7.1 <>... We don't accept connections
> from unresolvable addresses. Fix your reverse DNS for XXX.XXX.XXX.XXX, or
> use your ISP server.)

It would be easier to trouble-shoot this if you disclosed the address. 
For now, let us denote the numerical IPv4 address with A.B.C.D.  The 
error message specifically means that the name 
cannot be resolved.  If the address refers to a computer that is 
maintained by you, you should change its configuration in such a way 
that it does not directly try to initiate SMTP connections to outside 
hosts; instead, it should use send the messages to the SMTP server of 
your Internet service provider (ISP) for relaying.  And that server 
should definitely have a reverse DNS entry.  In my opinion (and probably 
also in the opinion of our network administrators), all visible IP 
addresses should have reverse DNS entries.


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