I have recently received a question that what RBL is used by Microsoft. I searched through many Microsoft articles but but none of them says about any RBL, but suddenly I came across a smtp response, which clarified that Microsoft is certainly using services of spamhaus. Hence their sender.office.com is using spamhaus in backend.
Here is the smtp conversation when i did telnet to alwayslearn-xyz.mail.protection.outlook.com on TCP 25 and received this errror.
220 MA1IND01FT004.mail.protection.outlook.com Microsoft ESMTP MAIL Service ready at Thu, 25 Jul 2019 18:58:15 +0000
250-MA1IND01FT004.mail.protection.outlook.com Hello [18.104.22.168]
mail from: firstname.lastname@example.org
250 2.1.0 Sender OK
550 5.7.1 Service unavailable, Client host [22.214.171.124] blocked using Spamhaus. To request removal from this list see https://www.spamhaus.org/query/ip/%5B126.96.36.199%5D (AS16012612) [MA1IND01FT004.eop-IND01.prod.protection.outlook.com]
Thank you for reading !