(Stolen from Michael's signature)
From: mailop [mailto:mailop-boun...@mailop.org] On Behalf Of Gilles Chehade
Sent: Wednesday, September 21, 2016 6:02 AM
Subject: [mailop] anyone from Microsoft around ?
I'm lead developer of an opensource MTA called OpenSMTPD.
We run a mailing-list for our project with very low volume, exchanging a few
thousands messages each month to around 400 people, very few of them being
hosted at big hosts, all of them having subscribed voluntarily.
In addition to this, we use a few mailboxes at major hosts and send some mails
every now and then to ensure we didn't break the smtp engine, this usually
amounts to less than 10 mails / month per big ISP.
All of these mails respect all best-practices that we know of:
- they are sent from long existing domains;
- they are rate-limited despite low volume;
- they are DKIM/DomainKeys signed;
- DNS is properly configured with valid DNS/rDNS for the one IP address;
- IP address is the same as the MX accepting mail for the domain;
- SPF is properly declared, so is DMARC;
I checked senderscore and we actually send so few volume we don't even have a
reputation visible there.
I've started receiving complaints about users receiving their messages in the
spambox only at microsoft-hosted domains. No problem for gmail, yahoo, orange
and others, just microsoft.
I did some testing, and it turns out that even the simplest mails will end up
spamboxed no matter what machine or domain I use to send. The reason advertised
in the Microsoft appended domains may vary if I turn off DKim, strip some or
all Received lines, but basically no matter my configuration, mails will not be
I'm wondering if there is something wrong in the format of our headers and if
this could affect users of our software disregarding the kind of mails they
send with it. I've been tackling this for hours before contacting the mailing
Any help would be greatly appreciated, I'm running out of ideas :-)
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