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The only thing I can recommend at this point is to maybe create a brand new App Registration in Entra and following the osTicket OAuth2 documentation exactly as it states. Also, you should now be using the Scopes of offline_access https://outlook.office.com/IMAP.AccessAsUser.All https://outlook.office.com/POP.AccessAsUser.All https://outlook.office.com/SMTP.Send
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As long as you modify the plugin as stated above, use the correct Scopes, and authenticate as the correct user you should have no issues. I just retested with my O365 personal email and it's working as intended for both IMAP and SMTP using these instructions.
Cheers.