I've been having the same issue with my Outlook account. Been fighting with MS support for over 2 weeks and still nowhere with it. If you get further progress with their support let me know! 
Cheers.
OAuth2 - Microsoft setup
KevinTheJedi
Yes, I have opened the case with Microsoft, but they are point back to osTicket
strange, but I have found one post related to hybrid setup, maybe that's the issue, we are running this setup:
https://blog.thenetw.org/2019/05/13/using-client_credentials-with-microsoft-graph-in-hybrid-exchange-setup/
ActAsPermissions and set it to AppOnlyPermissions
If you are in a hybrid environment, you might check this:
Cause
This error can occur if the mailbox is on a dedicated Microsoft Exchange Server and is not a valid Microsoft 365 mailbox.
Resolution
To get a valid Microsoft 365 mailbox, submit a request to your Exchange or Global administrator to migrate the mailbox account. Users who don't have administrator permissions can't migrate accounts.
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Using a personal outlook account hosted by microsoft (I am also the "admin" as I created and own the account - nothing else is attached no other user owns this account). No special setup so none of that will work for me.
Cheers.
I'm beginning to wonder if personal accounts do not have the full API access needed as a full fledged O365 tenant.
Could be the case but why would MS enforce Modern Auth across the board if personal accounts can't use it? Kind of counter-intuitive and will make people migrate away from them. 
Cheers.
KevinTheJedi
When I set up the plugin, it successful saves the settings, and it shows Azure successful login
When I go back to the plugin, it switches back to Authorization
Authentication is for User/Agent authentication against your OAuth2 provider. Authorization is email authentication. Also, you cannot update an instance for email authorization as when it loads the form on the email side it will overwrite with authorization data.
Cheers.
@KevinTheJedi
When I run Integration assistant, everything shows fine
I get it now:
array ( 'code' => 'ErrorAccessDenied', 'message' => 'Access is denied. Check credentials and try again.', )
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KevinTheJedi
Are you sure EmailAddresses is the correct attribute?
Answer: I am not sure, but I was trying email, and mail, and added a custom attribute
still no go
Which Graph URLs and scopes, I should be using?
I tried this:
offline_access https://graph.microsoft.com/IMAP.AccessAsUser.All https://graph.microsoft.com/POP.AccessAsUser.All https://graph.microsoft.com/SMTP.Send
and got errors: array ( 'code' => 'InvalidAudienceForResource', 'message' => 'The audience claim value is invalid for current resource. Audience claim is \'https://graph.microsoft.com/\', request url is \'https://outlook.office365.com/api/v2.0/me\' and resource type is \'Exchange\'.', 'innerError' => array ( 'oAuthEventOperationId' => '5c2f112a-237b-1cf0-9fa3-18b854eacf28', 'oAuthEventcV' => 'mG0x7T+u84eyGvKdW3h6Ig.1.1', 'errorUrl' => 'https://aka.ms/autherrors#error-InvalidResource', 'requestId' => 'cs313d50-8f2f-d2f8-b12e-f11s5b239a17', 'date' => '2022-08-16T14:04:51', ), )
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Because when you use Graph Scopes you also have to use the Graph Resource Details Endpoint https://graph.microsoft.com/v1.0/me.
Cheers.
KevinTheJedi
Yes, I just changed it to Graph Resources and got a new error:
array ( 'code' => 'Authorization_RequestDenied', 'message' => 'Insufficient privileges to complete the operation.', 'innerError' => array ( 'date' => '2022-08-16T14:20:00', 'request-id' => 'a2f24820-a560-1nb1-ad50-a9n651351640', 'client-request-id' => 'a2f24820-a560-1nb1-ad50-a9n651351640', ), )
Did you add all the API permissions to the app? You need to make sure User.Read.All and such are enabled for the application.
Cheers.
You may also need to Admin Consent to those permissions and scopes as well to allow it.
Cheers.
KevinTheJedi
Yes, I have, here is what I have, unless I am missing something
ramrajone User.Read.All
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KevinTheJedi
ok, I got a little far this time, with little success, but not functioning yet
When I add an email address: get Authenticate failed, which is normal, because I have to go into config
Then, it blanks out all the settings, like Hostname, Port Number, Protocol
I just have to re-enter it and save it.
After that, I get Authentication failed, when enabling Email Fetching
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Yea we are working on stashing and recovering that data when you get directed away from that page. That change will be part of RC4.
Now you are where I am. I get AUTHENTICATE Failed with Graph scopes but cannot even get a token with outlook scopes. Their official docs say to use the outlook scopes but their other docs say not to use them as they are deprecated and you should use graph instead. So I contacted MS support and after 3 weeks still nowhere with this issue.
Are you using a personal outlook/exchange email by chance? Everyone else on the forum seems to have O365/Exchange/Outlook setup and working but us with personal accounts cannot proceed.
Cheers.