Hotmail/Outlook Block List S3140 blocks all new email servers.

Yes, I'm having the same problem.

Im sending account verification emails from Sendgrid and they are outright being blocked by all microsoft products. My customers are not able to find these emails in their junk or spam folders either - it's a hard block.

We have lost 75 customers so far because they have not been able to verify their account :)

What can we do? 

It's not just new emails that are now blocked.  I've run my own email server since the 1990's.  I set a new one up about a year ago and up until about a month ago, it worked just fine talking to Hotmail.  Now, all of a sudden, it's blocked.  I wouldn't care except my attorney is on Hotmail and I've got a legal action in process right now.

When I ask for help the tech support guy said "too many complaints about spam" and that "I should check my technical configuration."  Too bad Microsoft can't tell me which technical standards I've violated.  Nobody has EVER complained that my mail server has sent spam because it doesn't send spam.  I've got SPF, DKIM, and DMARC all configured properly, at least according to Google and ProtonMail, and the sad part is that my IP address is blocked, which isn't related to SPF or DKIM.  I'm running a server whose forward and reverse name resolution matches and has a certificate with the correct forward name.  When it gets a 500, it stops trying and I don't send any email automatically.  When I try to sign up to where they say I can find out more and perhaps get off the list, it doesn't work.  At all.

Is there anybody at Microsoft who understands how to set up email or even a freaking web site sign-up?  You'd think a Fortune 50 company would have a better web site than some 14 year old could set up in his basement.

Of course I'm a little cheesed off!  Did I mention that I'm in the middle of a legal action?  Did I mention that my lawyer's email is on Hotmail?  This couldn't have happened at a worse time for me.

Facing the same problem here - first I thought the SPF information was not correct, it all check out. 

This is a ridiculous block. Looks like negligence/ignorance or an effort to make the life of smaller providers even harder.

Really without clue to how raise this to someone that can make decisions - other than some bot.

Im facing the same issue.

I moved some of my mail hosting to the Microsoft Azure Cloud in Switzerland North.

Every single static public IP i tried (About 5) is blocked by Microsoft spam List S3140.

Why does Microsoft block its own IPs?

I tried to get it unblocked with the Microsoft costumer support but we could not resolve the issue.

I think the whole Azure subnet is on the block list.

Something like:  51.103.xxx.xxx

Also being impacted sending from an Azure hosted server.  Please advise on potential corrective options.  Already filled out Support Request.  No response...

Note: responses went to junk mail.  Forgot to check that....

I'm having the same problem. I'm hosting my own email server, I'm on no blocklists according to MXToolbox, and have all the required reverse DNS, DMARC, etc configurations. My host is not an open relay nor is it being used to send bulk email (it's for my consulting company's domain) but MSN is blocking it with a 550 5.7.1 message identical to reported in the OP.

I am also seeing this issue with my single small private virtual server. I only have a handful of low-use domains, sending maybe 10 emails a day combined.

We have a dedicated fixed IP with correct forward and reverse DNS, as well as properly configured SPF, DKIM and DMARC. Our firewall is correctly configured to block access to things such as SSH from unauthorised IP address. I have checked the logs and we don't have any auto-forwarding going on and no excessive outbound emails to anywhere.

I have a ticket in with Microsoft but they initially said there was nothing they could do and we were banned due to spam, or people reporting emails coming from our IP address as spam.

I am baffled as we hardly send any emails to Outlook.com/Hotmail.com addresses!

We are having the same problem

we use spf, dkim and dmarc. 

We are making use the Smart Network Data Service (SNDS) since years and  looking at the compliance rate during the last 30 days it has always been <0.1%. 

We tried to get the IP delisted and got this answer:

We have completed reviewing the IP(s) you submitted. The following table contains the results of our investigation.

Not qualified for mitigation