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Microsoft Email Shenanigans

20 May 2020

Last week, emails from one of our web servers started being rejected by Microsoft mail servers, meaning that a few of our websites, including an extremely popular e-commerce site were unable to send to accounts @outlook, @hotmail, and @live.

The block was applied without warning, and apparently without justification, as we are not in the business of sending spam emails, or even promotional emails, from the affected websites.

Following a previous incident with Microsoft a few years ago, we have dutifully subscribed to their Junk Mail Reporting Program (JMRP), which notifies us when any emails from our servers are flagged as spam, and their Smart Network Data Services program (SNDS) program, which provides up to date reports on deliverability issues. We also comply with various RFC and policy guidelines.

So you'd think we'd be in the clear?


Chirp: please unblock our IP address. We've done nothing wrong, and no issues have been reported via either JMRP or SNDS. Also, we are not on any global block lists, or having problems with any other recipients.

Outlook.com Deliverability Support: our investigation has determined that you do not qualify for mitigation. We recommend you comply with Outlook.com policies, and subscribe to JMRP and SNDS.

Chirp: we are complying with your policies, and have already subscribed to JMRP and SNDS, which show no problems. We are not blacklisted anywhere, and have a Sender Score of 99/100. Please unblock our IP address.

Microsoft Customer Support: recent activity coming from your IP has been flagged by our system as suspicious, causing your IP to become blocked. I have conducted an investigation into the emails originating from your IP space and have implemented mitigation for your deliverability problem.

We suggest you sign up to JMRP and SNDS, or the Sender Score Certified Mail program [which may or may not be a scam charging thousands of dollars for little or no benefit].

Chirp: thank you, but can you please tell us why we were blocked, so that we can prevent it from happening again.

Microsoft Customer Support: I am unable to provide any details about this situation since we do not have the liberty to discuss the nature of the block.

Chirp: ...

Anecdotally, we have heard that Microsoft was in the process of making changes to email handling, and that other organisations were affected around the same time we were, but it's a strange way to run a railroad.

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