Announcing: Office 365 endpoint categories and Office 365 IP Address and URL web service

ankit1990 It would help if you shared what the customer is trying to achieve by blocking IP Addresses for SMTP. As Steve points out there is no correlation between the IP Address assigned to a server and the origin of an email. SMTP email can get routed anywhere by providers.

Office 365 SMTP connections always come from IP Addresses identified in the Sender Protection Framework. Read about it at https://docs.microsoft.com/microsoft-365/security/office-365-security/how-office-365-uses-spf-to-prevent-spoofing

SMTP sender IP Addresses are a subset of what is published at http://aka.ms/o365ip. Find specific SMTP source IP Addresses for Office 365 with this command on Windows: nslookup -type=TXT spf.protection.outlook.com

Paul