In order to provide the best-in-class encryption and security to customers, Microsoft Office 365 is removing support for TLS 1.0 and 1.1 as of October 31, 2018, which may weaken protocols and affect printer connectivity to Office 365.
By October 31, 2018, all client-server and browser-server combinations should use TLS version 1.2 or newer to ensure connection without issues to Office 365 services.
For more information, go to Microsoft Support document Preparing for the mandatory use of TLS 1.2 in Office 365. (4057306)
Due to this decision from Microsoft, a few older Samsung MFPs with secure SMTP (email feature) that are using OpenSSL library with a TLS1.1 or older version cannot connect to Microsoft Office 365 (SMTP server).
