Date: Sun, 20 Jan 2013 23:41:45 -0500 From: Eitan Adler <lists@eitanadler.com> To: Warren Block <wblock@wonkity.com> Cc: freebsd-doc@freebsd.org Subject: Re: documenting the requirements for FreeBSD.org to send mail Message-ID: <CAF6rxg=j0tfcv12oNP%2BjwBLd0GFXvz%2Bvq4gc3%2BM6F-dV%2B2M5Lw@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.1301171705140.90355@wonkity.com> References: <CAF6rxgm-TbOMpr0t=NDvtJ3RLa5avAMt_5%2B%2BZTgAh1EoofHXnA@mail.gmail.com> <alpine.BSF.2.00.1301171705140.90355@wonkity.com>
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On 17 January 2013 19:06, Warren Block <wblock@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
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