documenting the requirements for FreeBSD.org to send mail

[Eitan Adler]

On 17 January 2013 19:06, Warren Block <wblock at wonkity.com> wrote:
> Typo (conneting).  But that sentence is confusing.  IP address to domain and
> back to IP address which must match the original IP address?

It was a poor attempt at condensing the following:

===
The problem I have with the above is that it appears to imply that
DNS (only) establishes a one-to-one mapping between hostnames and
IP addresses.  This is not the case.

In particular, it is not at all unusual for multiple hostnames to
resolve to the same IP address; it is also not at all unusual for
one hostname to resolve to a set of many IP addresses.

Thus, it is possible to make use of these properties even if one
lacks control over the in-addr.arpa zone for one's IP adddress, as
long as there is a PTR record that points to a hostname, one of the
IP addresses of which is the IP address currently being used for
the SMTP conversation:

mx1(8.3-P)[1] host mx.catwhisker.org
mx.catwhisker.org has address 198.144.209.73
mx1(8.3-P)[2] host 198.144.209.73
73.209.144.198.in-addr.arpa domain name pointer m209-73.dsl.rawbw.com.
mx1(8.3-P)[3] host m209-73.dsl.rawbw.com
m209-73.dsl.rawbw.com has address 198.144.209.73
mx1(8.3-P)[4]

As long as the above "looks consistent," (for a particular SMTP client),
that meets the DNS requirements.  And the above does meet the requirements.
===
-- 
Eitan Adler