All guest users in Azure AD will have UPN is the same format that you have mentioned above (rambo.jan_test.com#EXT#@abc.onmicrosoft.com).
However, you can also use below powershell command to get the desired output that you are looking for,
Get-AzureADUser -All $true | where {$_.userPrincipalName -like "#EXT#"}
To run above command, you will need Azure AD module installed.
If you already have Azure AD module you can follow below steps to get the output,
- Run command "connect-AzureAD"
- Enter the Global admin credentials.
- Now run command Get-AzureADUser -All $true | where {$_.userPrincipalName -like "#EXT#"}
- You can also run command Get-AzureADUser -All $true -filter "usertype eq 'guest'"
Let me know if you have any further questions.
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