Getting an IP address delisted and whitelisted by Microsoft after being on an IP blacklist

2024 Guide: How to get your IP address removed & delisted from the Microsoft Hotmail, Outlook etc. blacklist

We recently took on the task of getting a client’s new IP address removed from a few blacklists. The trickiest part was dealing with Microsoft so that the client’s emails to Hotmail/Outlook etc. inboxes didn’t bounce back as undelivered.

Blacklisted Digital Ocean IP address

The problem arose when the client purchased a VPS from Digital Ocean to host their website and emails. Unfortunately, they hadn’t realised that the IP that was assigned to them had previously been used to send out spam emails. This became apparent when they checked it using a couple of free IP blacklist-checking tools such as MX Toolbox and HetrixTools. Of course, this isn’t exclusive to digital Ocean, it can also happen with other VPS provider such as Linode, Vultr, Amazon Web Services (AWS), Google Cloud Platform (GCP), Microsoft Azure, UpCloud, Scaleway, Hetzner Cloud and OVHcloud.

Check DNS configuration

The client didn’t want to ditch their VPS and hunt for a clean IP so, firstly, we had to make a few DNS tweaks to ensure that sent emails were achieving 10 out of 10 with the awesome free email testing tool at mail-tester.com.

This typically involves making sure the email passes various authentication and configuration tests like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), DMARC (Domain-based Message Authentication, Reporting, and Conformance), PTR (Pointer Records), rDNS (Reverse DNS), and checking the hostname. These are key elements in verifying the legitimacy of an email sender and protecting against spam and phishing attacks.

Getting whitelisted from various IP blacklists

When all these were in place, we then got the IP removed and delisted, or whitelisted, from all the usual blacklists including Spamhaus (Spamhaus are a big hitter and are used by Google for their Gmail service). Consequently, within 36 hours, emails began arriving in Gmail inboxes – Yay, sweet!

But… with Hotmail and Outlook accounts, it was still a problem. They weren’t even able to make it to a Hotmail spam folder but were still being rejected outright and bouncing back as undelivered immediately. Here’s an excerpt of the message:

<>: host
eur.olc.protection.outlook.com[104.47.13.33] said: 550 5.7.1 Unfortunately,
messages from [xxx.xxx.xx.xxx] weren’t sent. Please contact your Internet
service provider since part of their network is on our block list (S3140).
You can also refer your provider to
http://mail.live.com/mail/troubleshooting.aspx#errors.
[XXX3.eop-eur04.prod.protection.outlook.com

Action: failed
Status: 5.7.1
Remote-MTA: dns; eur.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1

Try the “Office 365 Anti-Spam IP Delist Portal” first

As above, the first thing to try is to see if your IP is listed by the Office 365 Anti-Spam IP Delist Portal. If it isn’t (and our client’s wasn’t) then like us, you’ll need to dig a little deeper.

Deciphering error/bounce clues S3140 and 550 5.7.1

The error code S3140 in a bounced email message typically indicates that part of the sender’s network is on a block list of the email service provider, such as Outlook.com, Hotmail, etc. This message often accompanies a 550 5.7.1 error code, which further explains that messages from the sender’s IP address were not sent because the IP is on a block list.

Unfortunately, this issue usually requires the sender to contact their Internet service provider (ISP) or, in this case, their VPS provider, to start the resolution process. It’s a common problem when an IP address is suspected of sending spam or has been used for suspicious activities. And, since the client had only just acquired the IP, this looked to be the case.

Getting delisted from @outlook @hotmail @live @msn email addresses

So now came the time to bite the bullet and knuckle down to it – there were no easy shortcuts. So, in order to get delisted/removed from Microsft’s blacklist, you first have to log in here.

You’re then presented with a rather lengthy form that must be filled in. This is what we did and this is the reply we got:

Hi ,
Thanks for your patience while we investigated your request.
Below your IP address(es) and their status(es) are listed.

Not qualified for mitigation

[xxx.xxx.xx.xxx]

The IP(s) above do not qualify for mitigation.

Oh dear, that’s not a good start. If this happens to you and you see “Not qualified for mitigation”, don’t despair; persevere. So we replied, informing Microsoft that our emails were passing SPF, DKIM and DMARC, we weren’t sending spam and wanted a reconsideration since the IP had only recently been acquired. We got this reply:

Hello,
Thank you for contacting the Outlook.com Deliverability Support Team.

In-order for us to investigate further, please provide the required documents (email from ISP as PDF attachment and Invoice copy) supporting the Proof of Purchase for the IP address [IP ADDRESS]

We will continue our investigation as soon as we have the required information.
Thanks again

OK, so that’s some progress at least. The client then provided a Digital Ocean invoice but it only showed the hostname and not the IP so they also included a screenshot with their reply, which also showed the date the IP was acquired. Here is the response they got:

Hello,
Thank you for contacting the Outlook.com Deliverability Support Team.

Please request your ISP/ ESP to send you an email in the below format. Once received please forward the same as an attachment to us for further investigation.
“The IP [xxx.xxx.xx.xxx] was assigned to [example.com/client’s name] on DD/MM/YYYY”
Thanks again

We then advised the client to raise a support ticket with their VPS provider, Digital Ocean, asking them to provide the specific information exactly as requested by Microsoft. To their credit, DO responded very quickly, were extremely helpful, and duly did exactly as asked. This email was saved to PDF and then sent to Microsoft as an attachment. This was their response:

Hello,
Thank you for contacting the Outlook.com Deliverability Support Team.

We will be looking into this issue along with the Escalations Team for the IP address [xxx.xxx.xx.xxx]. We understand the urgency of this issue and will provide an update as soon as this is available.
Thanks again

BAM! Within 24 hours the IP was completely unblocked by MS.

The moral of the story

Cleaning a dirty IP with a baaaad reputation may require a bit of effort on your part, especially if it’s blocked from sending to @hotmail @live @msn @outlook @live email addresses. But, if you’re certain your IP is now squeaky clean, it shouldn’t be a problem, and you can’t blame Microsoft for running a tight ship in order to keep their network as spam-free as possible.

Additional tags: Digital Ocean, Linode, Vultr, Amazon Web Services (AWS), Google Cloud Platform (GCP), Microsoft Azure, UpCloud, Scaleway, Hetzner Cloud, OVHcloud

2 thoughts on “2024 Guide: How to get your IP address removed & delisted from the Microsoft Hotmail, Outlook etc. blacklist”

  1. Hi. How long did it take from start to finish of the whole process? My IP has been blacklisted and MS sent me the not qualified for mitigation message. If I appeal it, how long will it normally take to get my IP unblocked?

    Reply
    • Hi Mike. It was within 24 hours. Oddly, they didn’t send a reply, they just unblocked the IP. Well, they did send a blank email which I assume should have been the “you’ve succeeded” one 🙂

      Reply

Leave a comment