Re: [dmarc-ietf] Thoughts on choosing N

[Scott Kitterman <[e-mail]>]

On Tuesday, April 16, 2024 2:24:07 PM EDT John Levine wrote:
> It appears that Scott Kitterman  <[e-mail]> said:
> >In the case of a.b.c.example.com and example.com is in the PSL, the DMARC
> >records in a.b.c.example.com (if present) and example.com (otherwise) are
> >consulted.  The only way to get to b.c.example.com or c.example.com would
> >be to add them to the PSL.  These are what I meant by intermediate
> >records.
> 
> I get that but in fact there are lots of PSL records underneath .com, more
> than 900 of them.
> >I don't find cases where it looks like such things have been added to the
> >PSL, ...
> We know there aren't any in the PSL more than 5 levels deep but there
> are plenty shallower than that. I have no idea how many of them are
> used for mail but a lot of them look plausible.

...

Yes.  I think there's a clear argument for n=5.  The claim is we need a bigger 
number.  If that were true, I would expect to see longer PSL entries that are 
plausibly related to email.

Scott K