As previously communicated in MC126199 in December of 2017, to provide best-in-class encryption, and to ensure our service is more secure by default, we are moving all of our online services to Transport Layer Security (TLS) 1.2+.
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In the two communications referenced above, we had indicated that we would be removing support for TLS versions less than 1.2 from our online services, beginning March 1, 2018. After receiving valuable feedback from administrators like you, we have decided to extend the deadline for upgrading to TLS 1.2 or later to October 31, 2018.
As of October 31, 2018, Microsoft Office 365 will no longer support TLS 1.0 and 1.1.
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.
We recommend you proactively address weak TLS usage by removing TLS 1.0/1.1 dependencies in your environments and disabling TLS 1.0/1.1 at the operating system level where possible. Begin planning your migration to TLS 1.2+, today.