IPv6 isn't SMTP

Thu Mar 27 00:47:20 UTC 2014

On Mar 25, 2014, at 8:31 PM, Cutler James R <james.cutler at consultant.com> wrote:

> 3.  Arguing about IPv6 in the context of requirements upon SMTP connections is playing that uncomfortable game with one’s own combat boots.  And not particularly productive.

That is one of my two big take-aways from this conversation. The other is that operators of SMTP MTAs should implement RDNS for them, which I thought we already knew.

To my knowledge, there are three impacts that IPv6 implementation makes on an SMTP implementation. One is that the OS interface to get the address of the next MUA or MTA needs to use getaddrinfo() instead of gethostbyname() (and would do well to observe RFC 6555’s considerations). Another is that, whether on an incoming or an outbound connection, when the application gets its own address from the OS (binary or as a character string), it needs to allocate more storage for the data structure. The third is that it needs to be able to interpret user at 2001:db8::1 as well as user at dns-name and user at 192.0.2.1. 

All things considered, that’s a pretty narrow change set.

Everyone here, no doubt, is clueful enough to implement RDNS for their MTAs. We know that there are people in the world that don’t implement it for IPv4. Yet, here we are, using SMTP/IPv4 to discuss this, and I don’t hear anyone saying that IPv4 isn’t ready for prime time as a result of the fact of some operators not implementing RDNS.

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