At the beginning, an application must be registered if this has not already been done.
You can create a new application in the Azure Active Directory under "App registrations" under "+ New registration".
Application configuration:
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Set API permissions as follows and grant admin consent.
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Configure "Authentication":
-"Add a platform"
-Enable "Allow public client flows"
-Save
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Create app role.
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Enable smtp client authentication
- Connect to your Exchange Online environment (Connect-ExchangeOnline)
- Get actual SMTP client authentication configuration for your mailbox (Get-CASMailbox -Identity alias@yourdomain.com)
- Enable smtp client authentication (Set-CASMailbox -Identity alias@yourdomain.com -SmtpClientAuthenticationDisabled $false)