As previously communicated in MC191153, beginning October 13, 2020, we will retire Basic Authentication for EWS, EAS, IMAP, POP and RPS to access Exchange Online. Note: this change does not impact SMTP AUTH.
We have published an updated blog with more information about this change - Basic Auth and Exchange Online – February 2020 Update
There are several actions that you and/or your users can take to avoid service disruptions on client applications, and we describe them below and in the blog. If no action is taken, client applications using Basic Authentication for EWS may be unable to connect after October 13, 2020.
Any application using OAuth 2.0 and connecting using any of these protocols, will continue to work without change or interruption.
[What do I need to do to prepare for this change?]
You have several options on how to prepare for the retirement of Basic Authentication.
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We have made a report that will help you identify any impacted users and client applications in your organization available to all tenants. The blog has details about using the report.
Please review the Blog to learn more about this retirement.