As of October 31, 2018, Microsoft Office 365 will remove support for TLS 1.0 and 1.1. This means that if you have issues connecting to Office 365 services because of weaker protocols, no support tickets would be generated.

By October 31, 2018, all client-server and browser-server combinations should use TLS version 1.2 (or a later version) to ensure connection without issues to Office 365 services. This may require updates to certain client-server and browser-server combinations.

If you do not update to TLS version 1.2 (or later) by October 31, 2018, you may experience issues when connecting to Office 365. If you experience an issue related to the use of an old TLS version after October 31, 2018, you will be required to update to TLS 1.2 as part of the resolution.

The following are some clients that we know are unable to use TLS 1.2. Please update your clients to ensure uninterrupted access to the service.

•  Android 4.3 and earlier versions
•  Firefox version 5.0 and earlier versions
•  Internet Explorer 8-10 on Windows 7 and earlier versions
•  Internet Explorer 10 on Win Phone 8.0
•  Safari 6.0.4/OS X10.8.4 and earlier versions

Source: https://support.microsoft.com/en-us/help/4057306/preparing-for-tls-1-2-in-office-365

This change comes in the context where of all major web browsers, including Google Chrome, Apple Safari, Microsoft Edge, Internet Explorer, and Mozilla Firefox, altogether announced October 15, 2018 to remove support for TLS 1.0 (20-year-old) and TLS 1.1 (12-year-old) communication encryption protocols in the first half of 2020.

See the official articles here:

Google: https://security.googleblog.com/2018/10/modernizing-transport-security.html
Microsoft: https://blogs.windows.com/msedgedev/2018/10/15/modernizing-tls-edge-ie11/
Apple: https://webkit.org/blog/8462/deprecation-of-legacy-tls-1-0-and-1-1-versions/
Mozilla: https://blog.mozilla.org/security/2018/10/15/removing-old-versions-of-tls/