Microsoft 365 Deprecated Connectivity
Prepare for “The RPCalypse”
In October 2017, the Office 365 email platform will deprecate the use of RPC over HTTP, the protocol used by Outlook clients to connect to mailboxes. The new protocol will be MAPI over HTTP (MAPI/HTTP).
The actions to take before then are:
No further action should be required as compatible Outlook clients will reconfigure themselves according to the Autodiscover protocol.
Office 365 SSL/TLS Support
In October 2020 (previously March 2018, then June 2020), Microsoft 365 will only support TLS 1.2. This means that some down-level clients will fail to connect, either via browser, Exchange Active Sync or MAPI over HTTP. These clients include:
Legacy Authentication Retirement
Devices such as multifunction printers and other apps which use authenticated SMTP to transmit messages via Microsoft 365 will not be affected.
Older Clients Unsupported
From October 21, 2020, Microsoft Outlook 2010 and 2013 will not be “supported” connecting to Microsoft 365 cloud services. This doesn't mean it won't work, only that Microsoft does not guarentee they will work.
Office 2016 and Office 2019 will be supported to October 2023.