What is the difference between a Sender Profile, Delivery Profile, and Send Classification in Marketing Cloud?

Sender Profile: Defines the From Name, From Email address, and optional Reply-To address used in a send. Multiple sender profiles can be created for different brands or teams.
Delivery Profile: Specifies the physical mailing address (required by CAN-SPAM), header/footer, and IP address pool used for sending. The delivery profile determines which IP addresses are used.
Send Classification: Combines a Sender Profile, Delivery Profile, and classification type into a reusable configuration. The classification type is the most important property:
— Commercial: Respects the global unsubscribe list. Used for marketing email.
— Transactional: Does NOT respect the unsubscribe list. Used for order confirmations, password resets, and other transactional messages where the subscriber must receive the email regardless of opt-out status.
Choosing the wrong classification type can lead to legal issues (sending commercial email to unsubscribed users) or subscriber experience problems.