Sendmail on a LAN

JD jd1008 at gmail.com
Tue Aug 17 21:25:07 UTC 2010


  On 08/17/2010 01:27 PM, Gordon Messmer wrote:
> On 08/17/2010 09:33 AM, JD wrote:
>> Re:  a.b.c.d ==>   valid.host.name
>> and valid.host.name ==>   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
> address.
>
> Let's finish your test:
>
> $ host smtp.gmail.com
> smtp.gmail.com is an alias for gmail-smtp-msa.l.google.com.
> gmail-smtp-msa.l.google.com has address 74.125.155.109
>
> 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 74.125.155.109
> 109.155.125.74.in-addr.arpa domain name pointer px-in-f109.1e100.net.
> $ host px-in-f109.1e100.net.
> px-in-f109.1e100.net has address 74.125.155.109
>
> 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 smtp.gmail.com
> Clients rarely do.  It's the servers to which you're going to try to
> deliver mail that will mind.
I see! Thanks for the heads up!
At any rate, I am having serious problem with an unwieldy router.
I just posted a message about that.



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