Since Microsoft will soon start to turn off Basic Authentication for Exchange Online, you’ll have to enable Modern Authentication client-side if you still have some machines running Outlook 2013 and want them to connect to Office 365. This is quickly done by adding some registry keys. Modern authentication is already enabled by default in Office 2016 and later versions.
This process will activate the Modern Authentication workflow for all the apps included in Office 2013 (Outlook 2013, Excel 2013, Word 2013, OneNote, etc.), not just Outlook.
While this procedure will allow you (for now) to connect to Office 365, it is critical to remember that connection to Office 365 and Exchange Online via Office 2013 is not supported anymore. You should update to a newer and supported version soon, as things might stop working without notice.
To enable the feature, either open an elevated CMD and paste these commands in or add the entries manually via Registry Editor.
CMD:
reg add HKEY_CURRENT_USER\Software\Microsoft\Exchange /v "AlwaysUseMSOAuthForAutoDiscover" /t REG_DWORD /d 1 /f
reg add HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity /v "EnableADAL" /t REG_DWORD /d 1 /f
reg add HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity /v "Version" /t REG_DWORD /d 1 /fREGISTRY EDITOR:
| Path | Value | Type | Value |
|---|---|---|---|
| HKEY_CURRENT_USER\Software\Microsoft\Exchange | AlwaysUseMSOAuthForAutoDiscover | REG_DWORD | 1 |
| HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity | EnableADAL | REG_DWORD | 1 |
| HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Common\Identity | Version | REG_DWORD | 1 |
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