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You need to enable SMTP sending from Microsoft 365 Admin Center
Go to User list, click on a user. Click on Mail tab, then Manage email apps, then check Authenticated SMTP. https://docs.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/authenticated-client-smtp-submission | |
| Search Keywords: SMTP, Send Mail, Email, Authentication, OATH2, Thunderbird | |