Re: IPv6 isn't SMTP

[Franck Martin <fmartin () linkedin com>]

On Mar 26, 2014, at 5:47 PM, Fred Baker (fred) <fred () cisco com> wrote:

> On Mar 25, 2014, at 8:31 PM, Cutler James R <james.cutler () 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.

It is in several industry recommendations cf for instance BCP at www.m3aawg.org 

> 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@2001:db8::1 as well as 
> user@dns-name and user@192.0.2.1. 

and user@2001:db8::1.25 with user@192.0.2.1:25. Who had the good idea to use : for IPv6 addresses while this is the 
separator for the port in IPv4? A few MTA are confused by it.

> 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.
There is some confusion between MX selection and address selection, I tried to document it, and resolve the ambiguities 
in http://datatracker.ietf.org/doc/draft-martin-smtp-target-host-selection-ipv4-IPv6/ (comments at apps-discuss () ietf 
org)

Remember 70 to 90% of email is spam, blacklists can drop as much as 75% of spam at connection time (an IPv6 blacklist 
has problems due to size and impact on DNS). If we mess up the transition of SMTP to IPv6, less than 1 out of 10 emails 
in your mailbox will be remotely interesting….

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