Microsoft Claims to Block IP Space When They're Not, to Reject Content/Senders

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I’m sure many of you have seen this error when sending email to Hotmail/Outlook:

Unfortunately, messages from [IPHERE] weren’t sent. Please contact your Internet service provider since part of their network is on our block list

Typically this has meant that your IP space is not clean, and that Microsoft has blocked it from emailing their service. At least, that has been the prevailing thought, that they would be honest with this messaging. It seems that this is no longer true. I have been able to confirm that Microsoft will return this error when blocking content or sender, under unknown conditions. I’ll show my work:

From my relay:

Mar 27 14:45:10 relay-direct3 postfix/smtp[22758]: 3AFE73F04C: to=<{removed}>, relay=hotmail-com.olc.protection.outlook.com[104.47.13.33]:25, delay=0.21, delays=0.04/0/0.13/0.03, dsn=5.7.1, status=bounced (host hotmail-com.olc.protection.outlook.com[104.47.13.33] said: 550 5.7.1 Unfortunately, messages from [185.234.75.10] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3150). You can also refer your provider to Troubleshooting. [HE1EUR04FT016.eop-eur04.prod.protection.outlook.com] (in reply to MAIL FROM command))

From the same relay one second later:

Mar 27 14:45:11 relay-direct3 postfix/smtp[22751]: C1B503F04C: to=<{removed}>, relay=grewada-nl.mail.protection.outlook.com[104.47.4.36]:25, delay=1.1, delays=0/0/0.48/0.66, dsn=2.6.0, status=sent (250 2.6.0 <{id removed}> [InternalId=2035814505849, Hostname=VI1PR10MB1901.EURPRD10.PROD.OUTLOOK.COM] 15682 bytes in 0.153, 99.524 KB/sec Queued mail for delivery)

From their support team just a few hours later:

We were unable to identify anything on our side that would prevent your mail from reaching Outlook.com customers.

So you see, it is now true that Microsoft returns errors that are misleading and false, and this is as close to their own admission as we’ll probably ever get.

Thank you for listening :heart:

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Maybe their doing some weird greylisting where your on a very temp naughty list, and if you retry the same email shortly after your get accepted?

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The same emails seem to get rejected, but neighboring emails go through fine. So one sender might see it with some consistency, but a neighboring customer goes through every time from the same relay IP.

At least that’s my takeaway thus far.

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Probably 185.x.x.x IP space. I have heard from others that they don’t like e-mail coming from this space.

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Interesting. If only they would be open about it :frowning:

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I know outlook don’t like IP ranges of some provider, werid they dislike 185.x.x.x any reason why.

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You’d have to ask them. I’ve heard that they have been known to impose restrictions on that /8 for no reason other than it is in that /8.

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mrowe@elrond:~$ ifconfig | grep 185
        inet 185.191.xxx.xxx  netmask 255.255.255.248  broadcast 185.191.xxx.xxx

As a dweller in this IP space, I feel personally attacked. Who should I sue?

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