Issue: Emails sent to Hotmail or Outlook are bouncing with error message like,
Action: failed
Final-Recipient: rfc822;[email protected]
Status: 5.0.0
Remote-MTA: dns; hotmail-com.olc.protection.outlook.com
Diagnostic-Code: smtp; 550 5.7.1 Unfortunately, messages from [192.168.100.2] 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 http://mail.live.com/mail/troubleshooting.aspx#errors. [DB8EUR06FT054.eop-eur06.prod.protection.outlook.com 2024-02-07T10:16:59.270Z 08DC2775A52EF1AB]
Diagnosis: Your domain's email server's public outbound IP address, has been rate-listed or blocked by Microsoft, as your email reputation has been rated as poor, by the email recipients on Microsoft's network such as Hotmail, Outlook, MSN etc. Microsoft uses the blocked senders list to protect its customers from spam, spoofing, and phishing attacks. Your mail server's IP address, that is, the address your mail server uses to identify itself on the Internet, was tagged as a potential threat to Microsoft 365 for one of a variety of reasons. When Microsoft 365 adds the IP address to the list, it prevents all further communication between the IP address and any of their customers through Microsoft datacenters.
In a web browser, go to https://sender.office.com.
Follow the instructions on the page. Ensure that you use the email address to which the error message was sent, and the IP address that is specified in the error message. You can only enter one email address and one IP address per visit.
Click Submit.
The portal sends an email to the email address that you supply. The email looks something like the following:
Click the confirmation link in the email sent to you by the delisting portal.
This brings you back to the delist portal.
In the delist portal, click Delist IP.
After the IP address is removed from the blocked senders list, email messages from that IP address will be delivered to recipients who use Microsoft 365. So, make sure you're confident that email sent from that IP address won't be abusive or malicious; otherwise, the IP address might be blocked again.
Note: It may take up to 24 hours or results can vary widely before restrictions are removed.
When there's a problem delivering an email message that you sent, Microsoft 365 or Office 365 sends an email notification to let you know. The email notification is known a delivery status notification or DSN. The most common type of DSN is a non-delivery report (also known as an NDR or bounce message) that tells you that a message wasn't delivered. In certain situations, Microsoft must conduct additional investigations against traffic from your IP address. If you receive and NDR with code 5.7.511, you will not be able to use the delist portal. To request removal from this list, forward the above message to [email protected]. In the email to request removal from this list, provide the full NDR code and IP address. Microsoft will contact you within 48 hours with the next steps.
Microsoft has dealt with this issue extensively at https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/external-senders-use-the-delist-portal-to-unblock-yourself?view=o365-worldwide
Alternatively, you can make a support request to Microsoft at https://support.microsoft.com/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75 and request delisting of your IP address.