Re: sink.arpa question

[Jason Bertoch <jason () i6ix com>]

Tony Finch wrote:
> On Fri, 18 Dec 2009, Jason Bertoch wrote:
> > Isn't the fundamental problem that SMTP can fall back to an implicit MX?
> > None of these solutions will stop spammers from skipping MX records and
> > using direct-to-host connections.
>
> This has nothing to do with spam.

For the OP in the original thread, it dealt with spam.  I would also 
argue that spammers abusing the implicit MX, most often through 
forgeries, provides the biggest motivation to find a fix.

> > Shouldn't we just consider dropping the implicit MX back door as opposed
> > to getting creative with MX records that spammers will surely note and
> > avoid anyway?
>
> It's impossible to make that kind of incompatible change with an installed
> base of billions of users. 

I wouldn't call it impossible...difficult, maybe.  Do metrics exist on 
how many current installs still rely on the implicit MX?  Is the abuse 
of the implicit MX causing more harm than the effort it would take 
legacy DNS admins to specify an MX?