Note that the October 13 2020 deadline has been pushed back by Microsoft due to the COVID-19 situation:
"In response to the unprecedented situation we are in and knowing that priorities have changed for many of our customers we have decided to postpone retiring Basic Authentication in Exchange Online (MC204828) for those tenants still actively using it until the second half of 2021. We will provide a more precise date when we have a better understanding of the impact of the situation.
We will continue to disable Basic Authentication for newly created tenants by default and begin to disable Basic Authentication in tenants that have no recorded usage starting October 2020. And of course you can start blocking legacy authentication today, you don’t need us to do anything if you want to get started (and you should).
We will also continue to complete the roll-out of OAuth support for POP, IMAP, SMTP AUTH and Remote PowerShell and continue to improve our reporting capabilities. We will publish more details on these as we make progress."
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