On the other hand, this also means that if you want to use separate mailboxes (email addresses) for different tasks, you only need to configure and grant the permissions required for that functionality only (e.g. to configure a mailbox to use with Graph API, you don’t need any permissions related to SMTP or IMAP protocols). You also have the possibility to differentiate between incoming and outgoing connections, i.e. you can create an app registration (and a respective client credential) to configure a mail handler with, while you can create another registration to use for message sending only. In other words, the concept of mail providers allows for granular use and definition of permission scopes and the respective client credentials representing them.