Sendmail on a LAN

Gordon Messmer yinyang at
Tue Aug 17 20:27:28 UTC 2010

On 08/17/2010 09:33 AM, JD wrote:
> Re:  a.b.c.d ==>
> and ==>  a.b.c.d
> does not seem to apply to the google smtp server I use for Thunderbird.

You did your test entirely backward.  You did a forward lookup first, 
and then checked the PTR of the IP which was returned.  There is no 
requirement for a PTR to match every hostname that resolves to its IP 

Let's finish your test:

$ host is an alias for has address

The result of this test merely identifies an IP address.  Now, let's 
test to validate that the IP returns a PTR that resolves to the same IP:

$ host domain name pointer
$ host has address

Yep, totally valid.  That IP address has a PTR record, and the hostname 
contained in that PTR resolves back to the same IP address.  This host 
is properly configured.

> So, Thunderbird client does not seem to mind that
> reverse lookup does not match the name

Clients rarely do.  It's the servers to which you're going to try to 
deliver mail that will mind.

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