[EM] Missing messages (was: Re: Should we allow "voting off" this mailing list?)

[Kristofer Munsterhjelm]

On 2024-07-23 23:06, Toby Pereira wrote:
> I don't see most messages from Chris Benham or Kevin Venzke. I think it 
> might be something to do with us all using Yahoo, but you aren't so 
> there might be something else going on there.

I think that's due to different ISPs having different DMARC policies.

After some web browsing, I found the following explanation:

> There are three essential DMARC policy options: "none," "quarantine," and "reject".
> 
> - The "none" policy, also known as "monitor" tells the provider to
>   take no action.
> - The "quarantine" policy sends any unauthorized emails into a
>   separate folder, similar to a spam folder.
> - The "reject" policy tells the provider to block any unauthorized
>   emails so that they cannot reach recipients.

These tell the receiving mail host what to do if the DMARC check fails. 
They're set by DNS. For instance, for Yahoo:

$ dig -t TXT _DMARC.yahoo.co.uk
(...)
;; ANSWER SECTION:
_DMARC.yahoo.co.uk.	1800	IN	TXT	"v=DMARC1; p=reject; pct=100; 
rua=mailto:d at rua.agari.com; ruf=mailto:d at ruf.agari.com;"

p=reject sets the policy for any mails claiming to be from yahoo.co.uk 
to "reject". So the recipient should just delete them if they fail the 
DMARC check (as far as I understand). Fortunately for me, my provider 
just adds a penalty of 10 instead.

My own provider sets "p=quarantine". If Yahoo follows the policies 
literally, that should put my EM posts in your (Toby's) spam folder.

-km