[Mailman-Users] Many users unsubscribed at once (not by me)

Mark Sapiro mark at msapiro.net
Sun Dec 13 13:49:16 EST 2015

On 12/13/2015 09:49 AM, Larry Kuenning wrote:
> On 12/13/2015 5:14 AM, Hal wrote:
>> Seeing that 17 out of those 18 unsubscribed messages were sent from
>> Hotmail I can only assume the above was what happened. [etc]
> This sounds as if Hotmail has joined the villainous club formerly
> composed only of Yahoo and AOL, publishing a DMARC policy of "p=reject".
>  Can anyone else confirm that this has happened?

This is not the case. First of all, it doesn't say anything about
hotmail's DMARC policy. It only says that if these are DMARC bounces,
hotmail is honoring published DMARC policies.

In any case, here's hotmail.com's DMARC record.

_dmarc.hotmail.com.	3600	IN	TXT	"v=DMARC1\; p=none\; pct=100\;
rua=mailto:d at rua.agari.com\; ruf=mailto:d at ruf.agari.com\; fo=1"

p=none means no DMARC policy. This only means that ISP's should not
check DMARC for mail From: the hotmail.com domain. It does not mean that
hotmail won't check DMARC on incoming mail From: domains that do publish
a DMARC policy other than none, and in fact hotmail and other Microsoft
server do check DMARC and have from the beginning.

You can find the DMARC policy for any domain, e.g. example.com, by
querying DNS for a TXT record for the domain with _dmarc. prepended,
e.g. _dmarc.example.com.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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