Updated Readme

README.md

@@ -30,6 +30,8 @@ Add the configuration to your mail.php config file:
 ]
 ```
 
+Valid values for `tenant` are your tenant identifier (work & school accounts) or `common` for personal accounts.
+
 **Note:** This package relies on [Laravel's Cache](https://laravel.com/docs/cache) interface for caching access tokens.
 Make sure to configure it properly, too!
 
@@ -38,3 +40,9 @@ Make sure to configure it properly, too!
 To get the necessary client ID and secret you'll need to register your application and grant it the required
 permissions. Head over to [the Azure Portal to do so](https://docs.microsoft.com/en-us/graph/auth-register-app-v2)
 (you don't need to be an Azure user).
+
+Make sure to grant the _Mail.Send_ permission and to generate a secret afterwards (may be hidden during app registration).
+
+**Work & School accounts:** Granting your app the _Mail.Send_ permission allows you by default to send emails with every
+valid email address within your company/school. Use an [Exchange Online Application Access Policy](https://docs.microsoft.com/en-us/graph/auth-limit-mailbox-access)
+to restrict which email addresses are valid senders for your application.