[svlug] Can't Receive

[Rick Moen]

Scott DuBois wrote:

> 554 walimpinc14 bizsmtp  Connection rejected. Reverse DNS for
> 104.131.129.178 does not exist.)

There you go.  The 5xx SMTP result codes are the permanent-rejection ones,
by the way.  4xx is temporary rejection.  2xx is success.  There are others.

You would have gotten to this result a wee bit sooner if you'd done an SMTP
session manually using a telnet client, which is an essential skill for
anyone attempting to run an SMTP host.

> So if I hadn't been able to create that email account at the hosting
> company, I would have needed to ask them to set up a PTR record for me
> or set up rDNS for mail sent to the account to find the IP of the
> Postfix server? 

An SMTP host's IP _should_ have valid reverse DNS, yes.  It's an RFC
recommendation (RFC 19212, I think), not a requirement, but a pragmatic
necessity because many significant MTA sites simply will not accept from IPs
lacking a valid reverse, mostly as an antispam measure.  So, call it 'best
practices'.  And Postfix is apparently finicky about that.

> Is it normal for hosting companies NOT to automatically set up rDNS
> records?

Some do, some don't.  Failing to do it is sadly common, which is a bit sad
and unimpressive, because generating an in-addr.arpa zonefile of generic PTR
entries from knowledge of the IP netblock is a task you can do in about ten
minutes' thinking and experimenting with awk and the seq command.

For the ISPs / hosting outfits that haven't bothered, yeah, you have to send
them an e-mail requet or file a trouble ticket saying 'please do this PTR
for me'.  Alternatively, you can ask them to delegate authority over your
CIDR netblock to your nameserver, but the method of doing that is pretty
twisty and not worth the trouble unless you expect to want to change the PTR
entries on a significantly frequent basis.