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  2. PCTECH
  3. July 2006

Re: yahoo and "bulk" folder

Hi Dan -


I'm curious, how does a DNS not get set up correctly?


To give you essentially what Jim said, but from a slightly different angle:
The IP address of the sending mail server needs to have reverse DNS (a PTR record) which gives a fully qualified host name.
That fully qualified host name needs to have a regular DNS entries which gives back one or more IP addresses, of which one IP address is where you started.
The reverse DNS host name does NOT have to match the mail server's primary name. 

A real life example:
My mail server's primary name is mail.kensims.net. That's how it identifies itself in the EHLO command when it connects to another mail server. 
mail.kensims.net resolves to 24.234.149.199 and 65.40.146.221.
Most of my outgoing mail I relay through smart hosts. Unrelayed mail always goes out through IP address 24.234.149.199. 

24.234.149.199 has reverse DNS c.kensims.net (not mail.kensims.net).
c.kensims.net resolves to 24.234.149.199 only.
If 24.234.149.199 did not have a reverse DNS entry, that would be a problem. Or if it had a reverse DNS entry but that host did not resolve back to 24.234.149.199, that would be a problem.
Personally I do not reject email based on missing or incorrect DNS of any kind. I do reject on a lot of other things, but that's a whole different topic. Let me just say that the last piece of spam that actually made it on to my server was on 18-Dec-2005, and that's without any content filtering or the use of any external blocklists or any other external services. 

Ken
http://www.kensims.net/
Opinions expressed are my own and do not necessarily represent the views
of my employer or anyone in their right mind.

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