Ariel Costas

Microsoft's control over email

By Ariel Costas - October 16, 2021

A few weeks ago I posted on this website how Microsoft was blocking all my email. This situation hasn’t been fixed yet, and I found out it’s even worse than I thought.

I found out the message returned to Postfix after Microsoft rejected that email is only provided when messaging Outlook addresses (@outlook.tld, @hotmail.tld or but not when contacting another domain hosted on Outlook. In that cases, I send the email, it gets accepted as normal and don’t receive any complaint. But the recipients DON’T receive my emails, ever, not even on Spam or Junk.

I found out this when I wrote to my city bus company over a week ago, and I received no response to that email. A friend also wrote an email there, for another reason, and did receive a normal reply within two days. I was suspicious of this, so I wrote to someone I know’s Microsoft 365 email address, and the message was sent as usual; but they didn’t receive the email either. This means Microsoft is shadowbanning IP addresses from sending email to them.

Of course, they are free to do so if they want, because it’s their servers. But is it good that a corporation decides to cut someone off sending emails to many other people and companies? At the end of the day, I’m not emailing Microsoft but rather a family member, friend or company that host their email there.

If someone is sending you spam, it’s your choice as a user to send it to spam, delete it automatically or block the address that sends this to you. ISPs shouldn’t block more emails than those that don’t comply with SPF, DKIM and/or DMARC. Or, if they do block, to explain the reason why and provide a real way of getting unlisted.

Dear Microsoft, learn from Google

For once, I’m applauding Google for how it handles email (although they still do terrible things like parsing it to show it to you, or share info with three-letter agencies).

But at a strictly technical level they handle it as they should: they provide SMTP+IMAP access, comply totally with SPF, DKIM and DMARC (even the rua= sending you an email every day with how many emails failed DMARC) and all of that.

They don’t block your IP address totally, although they can flag your emails as spam even if everything is done correctly, but you eventually get delisted when they see your emails are not junk or people mark them as “not spam”.

So this is it, Microsoft, behave, please. You’ve been doing this bad thing for years, and it’s time to change. You’ll still do whatever you want, probably, so in that case FUCK YOU.