Re: [tlug] Yahoo.co.jp mail blacklisting

[Curt Sampson <cjs@example.com>]

On 2013-01-29 12:17 +0900 (Tue), Travis Cardwell wrote:

> Email infrastructure setup guide
> http://iafonov.github.com/blog/hardcore-email-infrastructure-setup.html

That's a terrible reference; it gets things wrong from the very start
and carries on that way.

Examples of errors:

] The basic question that any email receiving server should answer when
] it gets email sounds like this: ok, I got an email from this IP and it
] claims that is was sent from this domain, is it true?

Wrong. The basic question is, "is this mail likely to be spam." The
domain from which it was "sent" is not very relevant, and that phrase
doesn't even have any generally accepted meaning. For many of the
possible meanings of that phrase, however, the ostensible name of the
e-mail server will very frequently have no obvious connection to the
source of the e-mail.

] PTR record allows one to do a reverse lookup of IP address and find
] the domain bind to this IP address.

Not really. a PTR record allows one to look up a domain name (typically
a hostname, or more precisely, an A record) from an IP address. That
name may or may not have one or more A records, and an A record with
that IP address may or may not be present, though in a well configured
system those will both be the case.

] [your ip in reversed order].in-addr.arpa. IN PTR your-domain.com.

No, unless your-domain.com. has an A record for that IP address and it
happens to be easy to configure the in-addr.arpa record that way (it
often isn't because the control of that configuration typically resides
with another organization).

The important thing is that, when you look up a name from the
in-addr.arpa record for an address, and look up an address from that
name, the original address comes back. The names in between are
irrelevant. If we look at my mail server for example:

    $ host priv.dyadic.cynic.net.
    priv.dyadic.cynic.net has address 219.117.251.194
    $ host 219.117.251.194
    194.251.117.219.in-addr.arpa domain name pointer \
        219.117.251.194.static.zoot.jp.
    $ host 219.117.251.194.static.zoot.jp.
    219.117.251.194.static.zoot.jp has address 219.117.251.194

This is all just fine, and a perfectly usual situation, even though
someone armed with only the IP address is unlikely to be able
to find out that I myself happen to refer to my mail server as
"priv.dyadic.cynic.net."

The next bits are about DKIM and SPF, which I won't discuss except to
mention that I don't use them.

And I think I'll just give up here; a document that's gone this far
wrong this fast is not worth pursuing further.

cjs
-- 
Curt Sampson         <cjs@example.com>         +81 90 7737 2974

To iterate is human, to recurse divine.
    - L Peter Deutsch