[Cialug] Hostname issue

[Josh More]

Yeah, a lot of mail servers have taken to using the following logic.
I don't think it's in any of the RFC's (but the RFC's for SMTP are
such a mess that I stopped reading them years ago).

* Check reverse DNS against forward DNS for a match
* Open an SMTP session to the originating server to check its
advertised hostname
* Look at the TXT record for the domain to see if SPF allows the sender
* Look at the MX record for the domain to see if the sending IP is allowed
* Check the various blacklists
* Check the IP WHOIS to see if it comes from a residential block of
IPs  (This one *sucks* given IP block re-use.)
* Check the GEOIP list to see if the email is coming from a blocked
country (also a problem with IP block re-use.)

If any of the checks fail, sometimes the email is rejected, sometimes
it's greylisted, sometimes it's allowed.

That's why I don't run my own mail server anymore.

-Josh

On Tue, Nov 25, 2014 at 11:01 AM, L. V. Lammert <lvl at omnitec.net> wrote:
> On Tue, 25 Nov 2014, Josh More wrote:
>
>> $ dig barracuda.gilstermarylee.com MX
>>
>> On my system, this shows no DNS entry for barracuda.gilstermarylee.com
>>
>> The fallback SMTP host (A record) points to 75.149.203.77
>>
> That appears to be the A record for the Barracuda:
>
> ;; ANSWER SECTION:
> barracuda.gilstermarylee.com. 6964 IN   A       75.149.203.77
>
> I agree that the DNS is totally borked, .. *especially* if they want to
> use the Barracuda hostname externally.
>
> So, is it typical MTA practice to report "unknown" in the case of
> mismatched forward or forward/reverse? If so, that is an important clue
> that I have not seen anywhere in the docs before.
>
>         Thanks!!
>
>         Lee
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