Why is Microsoft blocking my emails?

Linode Staff

My emails are bouncing back, and I don't know why. I get the below message. What does it mean?

Please contact your Internet service provider since part of their network is on our block list

11 Replies

There are quite a few records that you will need to set up for a mail server. This will help validate your mail server to receiving mail servers. This Community site post from a couple of years ago is still rather relevant. It's a through explanation of how to set a mail server's records up.

I also recommend checking out the below resources for more information.

You may need to reach out to Support, if you find that you are still having issues sending email and it's only blocked by Hotmail/Outlook. We will be able to assist you with requesting a delisting from Microsoft. We will just need you to supply us with some information.

Please provide us with the following in your Support ticket:

  1. The full SMTP 5xx error message that you would have received when you were notified of this block from Microsoft. It should look something like this:
host mx3.hotmail.com[$MICROSOFTIPADDRESS] said: 550 SC-001
   (COL004-MC3F10) Unfortunately, messages from $YOURIPADDRESS weren't sent.
   Please contact your Internet service provider since part of their network
   is on our block list. You can also refer your provider to
   http://mail.live.com/mail/troubleshooting.aspx#errors. (in reply to MAIL
   FROM command)
  1. The domain that you were attempting to send mail from, and the domain that you were attempting to send to.

  2. Confirmation that you have a valid SPF Record and (rDNS) set up.

Microsoft will not accept mail from domains without a valid SPF record, and you are likely to have deliverability issues without valid reverse DNS set up. We can send a delisting request to Microsoft for you once we have that information and have ensured that your SPF and rDNS are set up correctly.

I hope this information helps!

They dont send any error anymore, they just drop the mail.

I use SPF/DKIM/DMARC. rDNS is set too.

@Tntdruid could you elaborate a bit more on that? We've very recently received reports of customers receiving such messages from Microsoft.

Made a myname@outlook.com account to test if mail gets there, they did not. Dont see any errors from outlook.com.

I have the same problem. I am receiving the following message.

SMTP: 550 5.7.1 Unfortunately, messages from [x.x.x.x] 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. [MW2NAM10FT006.eop-nam10.prod.protection.outlook.com]

The settings of SPF, rDNS, tested on the site mxtoolbox(https://mxtoolbox.com/). Would you help me.

@rbarbosa --

Unfortunately, without mind-reading capability, it's going to be difficult to figure out what, exactly, is wrong without a lot of trial and error. Microsoft is very inarticulate/capricious/litigious about their internal IT policies…and even less-articulate about their policies regarding customer-facing services.

They are also not immune to the good, ol'-fashioned screw-up. You know…the contractor in Bangalore changed something in the world-wide Exchange network s/he shouldn't have…

-- sw

I totally agree with @stevewi when it comes to the consumer-focused Outlook.com (previously Hotmail and related ilk.)

However I have been pleasantly surprised with sending mail to Office 365 users (the “cloudy” version of Exchange.) I’ve had several IPs from Linode that were only blacklisted by 365, but they bounced with a clear message and a web link that prompted me to submit the IP.

Within a day or two the block was removed and never had another issue with those IPs.

I had already checked how I mentioned in the previous message with mxtoolbox he searches in several RBL. I also tested using the websites you mentioned, I have dmarc dkim and spf and rdns I am sending and receiving to other domains like gmail, etc. less for hotmail. I sent it from another Linode server that is in the same region(Atlanta) and it worked.

@rbarbosa --

I wrote:

Unfortunately, without mind-reading capability, it's going to be difficult to figure out what, exactly, is wrong without a lot of trial and error.

Since you have access to an email server that works, I would do one of two things:

  1. use that server for your emails to Microsoft domains (easier); or
  2. figure out how your mail-server configuration is different than the one that is known to work (harder).

However, the situation you describe with the two servers in the same datacenter is not unusual in my experience. Are the two servers in the same subnet? Does mail from the two servers use the exactly the same SMTP "route" from source to destination?

Microsoft undoubtedly has developed proprietary sources of information that they use in making rejection decisions. Because of this, and their understandable reluctance to talk about internal IT security policies, you have no way of knowing exactly what the reason for rejection was…and Microsoft is never going to tell you either (you could always try asking but I wouldn't get overly hopeful about a response…or even an acknowledgement).

While mxtoolbox is a good toolset, the list of things it checks is not exhaustive. Because Microsoft uses proprietary sources of information in their decision-making process(es), mxtoolbox can never check those.

I suggest you get cracking on that trial-and-error process…you're going to be at it awhile (keep good notes). Don't be surprised when the thing you discover solves your problem stops working after awhile for no reason. Ditto for your "known-working" configuration exemplar. Unfortunately, Microsoft is flying this plane and, like in commercial airliners, there are locked, bullet-proof doors without windows between you and the pilot.

-- sw

Same thing has just started happening with my server as well. It was working fine 24 hours ago, so this is very recent.

At first I thought I had messed up my postfix setup (I've been rejecting spam emails sent to (not from) my server, but double checking has shown that it's all fine.

I've also used mxtoolbox and I'm not blacklisted (except via Hotmail/Outlook).

Cheers,
Darren

@cashdj --

You write:

Same thing has just started happening with my server as well. It was working fine 24 hours ago, so this is very recent.

Welcome back, my friend, to the show that never ends…

Back in my working days, I worked on a project that was a partnership with M$…partnership agreement & everything. M$ stole our idea(s) and marketed their own product…completely cutting us out. Needless to say, we abandoned our efforts. Fortunately, most of our IP was patented so M$ had to eventually pay us for a license to use it so we were able to recover some of the cost of this "relationship" (my former employer was particularly ferocious about this).

When we asked the M$ "VP of whatever Marketing" who was heading up their side of things what had gone wrong with the relationship and why they had done what they'd done, he said (and I'll never forget this): "You made a fatal mistake…you trusted us."

-- sw

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