Our emails are blocked by Hotmail and Outlook and Microsoft refuses to tell why ("I do apologize, but I am unable to provide any details about this situation since we do not have the liberty to discuss the nature of the block.") and asked us to check this link -> https://sendersupport.olc.protection.outlook.com/pm/troubleshooting.aspx

We've set up our SPF, DKIM and even DMARC (Gmail and mxtoolbox.com confirmed all as pass).

But under the link above there's a section below.

Confirm that your DNS is set up correctly Try connecting to mail.hotmail.com via port 25. If you are unable to connect, then attempt to telnet over port 25 directly to our email servers (MTAs). You can find the current list of our MTAs by querying "nslookup –q=mx hotmail.com" from a command prompt (this should work in a variety of Operating Systems). Currently, the addresses for these servers are mx1.hotmail.com, mx2.hotmail.com, mx3.hotmail.com and mx4.hotmail.com. If that doesn't work, try connecting directly to the IPs. If you are able to connect directly to the IP and not mail.hotmail.com, then it is likely that there is an issue with your DNS server.

I tried the above and my server can't connect to mail.hotmail.com via telnet 25. Is it necessary to confirm the DNS via telnet 25? I also nslookup of hotmail MX failed.

[root@server ~]# nslookup –q=mx hotmail.com
;; connection timed out; no servers could be reached

And the URL above also asked us to check our sender score at https://www.senderscore.org/get-your-score/ and our IP and domain name was clear (all green checkmarks).

  • The unfortunate truth is that MS may block you for any and all reasons. They will never tell you why. They will not unblock you. In the unlikely event that they do, you will be blocked again. Don’t deliver mails (directly) to Microsoft. // This looks like a corporate IT problem and as such would be off-topic here. – Daniel B Jun 23 at 15:05
  • @DanielB But some of my users are using hotmail.com or outlook.com emails, thus my site can't email them notifications like "You got a booking, etc", what should I do? – cilapo1541 Jun 23 at 15:11
  • Try using Mailgun, Amazon SES or similar services. Preferably on a plan with a dedicated IP address. – Daniel B Jun 23 at 15:15
  • @DanielB got it. Thanks so much. – cilapo1541 Jun 23 at 15:36
  • but seems you have a DNS issue. when I run the request nslookup -q=mx hotmail.com i got an answer: Server: Address: Non-authoritative answer: hotmail.com mail exchanger = 2 hotmail-com.olc.protection.outlook.com. so you might have issues on that particular server. – Zina Jun 23 at 18:00

The nslookup command is showing you that you are not able to hotmail.com name. May be:

  • The server don't have DNS configured correctly. Try to resolve another names like
    nslookup -q=mx gmail.com
  • The DNS Server is not correctly configured, you can try a different one, like:
    nslookup -q=mx hotmail.com
    nslookup -q=mx hotmail.com
  • There is a firewall blocking *.hotmail.com. Try pinging www.hotmail.com and also by their IP
   ping hotmail.com

If Hotmail.com had block you, check if you public IP or domain name had been blacklisted. Although from your description it does not seems to be the issue. I like to use the page: https://mxtoolbox.com/blacklists.aspx

| improve this answer | |
  • 1
    I did mention that I used mxtoolbox to check for blacklisting and we're not on the list. Anyway, your answer is detailed enough to garner a green checkmark. – cilapo1541 Jun 24 at 19:05

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