Resolve issue with email delivery to Hotmail/Outlook.com email addresses

Mail log is showing:

Failed to send email to XXXXXXXXXXX (xxxxxxxx@hotmail.com)

(5.7.1 Unfortunately, messages from [69.72.44.232] 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. [Name=Protocol Filter Agent][AGT=PFA][MxId=11BBC608ACCF6247] [MN1PEPF0000F0E4.namprd04.prod.outlook.com 2025-08-24T23:59:29.590Z 08DDE30456B9627E])

The most direct and correct URL for a sender to request delisting an IP address from Microsoft's blocklist is the Office 365 Anti-Spam IP Delist Portal.

The URL is: https://sender.office.com/ or

https://olcsupport.office.com/

This is the self-service portal specifically designed for senders who have had their IP address blocked from sending email to Microsoft's services (including Hotmail, Outlook.com, and Microsoft 365). You will need to provide the blocked IP address and an email address to receive a verification code.