Update: The full timeline for retirement of Basic Authentication in Exchange Online is now published in Basic Authentication Deprecation in Exchange Online – September 2022 Update.
In about 150 day...
Updated Sep 01, 2022
Version 5.0
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Jan089 thanks for pointing out this link!
I'll definitively look into it.
From what I read so far, our application has to be registered with the AzureAD of each customer who wants to use our application?
Then I have to use the MSAL to trade the configured username and password for an OAuth token which I have to store somewhere.
And then I also have to customize the authentication part of the POP3/IMAP protocol exchange to specify this SASL XOAUTH2 format and give the token instead of the user's password, right?
Sorry for asking such dumb questions but I can't really test anything with AzureAD since I don't have admin access and it's really hard to grasp on a purely theoretical base....