What are the send classification commercial vs transactional types, and why does the distinction matter?

Commercial send classification: Used for marketing and promotional emails. This type respects the global unsubscribe list — subscribers who have opted out will not receive the email even if they appear in the send audience. Required for CAN-SPAM compliance for commercial messages. Also respects publication list opt-outs.
Transactional send classification: Used for order confirmations, shipping notifications, password resets, and other operationally necessary emails. This type bypasses the global unsubscribe list — a subscriber will receive the email regardless of their opt-out status. Under CAN-SPAM, transactional emails are largely exempt from opt-out requirements because they contain information the recipient needs.
Why it matters: Using the wrong classification causes serious problems:
— Using Commercial for a transactional message: unsubscribed customers miss critical order updates.
— Using Transactional for a promotional email: you send marketing messages to people who have opted out, violating CAN-SPAM and GDPR, and risking high spam complaint rates.
Always audit send classifications during MC admin reviews.