Delegated permission acts with a user
A user signs in and consents, subject to tenant policy. Calls such as `/me/sendMail` act as that signed-in user. smtpify365 uses delegated Mail.Send and does not request tenant-wide application Mail.Send.
Application permission acts without a signed-in user
Application Mail.Send is designed for daemon or service scenarios and requires administrator consent. Its potential reach and operational controls differ materially from delegated access.
Match the model to the system
Use direct Graph with the appropriate permission model when developing a maintained application. A mailbox-specific delegated bridge fits a different problem: a user connects one mailbox for an SMTP-only client.