What are examples of transactional message types (receipts, alerts)?

Transactional emails fall into a few natural categories, all tied to something the recipient did or something that's happening to their account or order.

Order and purchase-related: Order confirmations, payment receipts, shipping notifications, delivery confirmations, invoices. These are the most common transactional emails and the least ambiguous. The recipient caused them by buying something.

Account and authentication: Password resets, email verification (like a double opt-in confirmation), login alerts for new devices or locations, two-factor authentication codes, account creation confirmations, username reminders. These need to arrive instantly. delays here destroy user trust.

Subscription and billing: Renewal notices, payment failure alerts, upcoming charge reminders, subscription cancellation confirmations, free trial expiration notices. These are transactional when they're informing someone about something happening to their account, not when they're selling them on upgrading.

Service and activity alerts: Appointment reminders, booking confirmations, event registration confirmations, status updates, usage alerts ("you've used 90% of your storage"), security notifications. Whether these are transactional depends on whether they're triggered by the user's activity or by your marketing calendar.

The edge cases: Re-engagement emails, win-back campaigns, product recommendation emails based on past purchases, review request emails. These feel transactional because they're related to something the person did. but they're primarily promotional. They're marketing emails that should be sent through your marketing infrastructure and subject to consent and unsubscribe requirements.

For the test that determines which category an email falls into, see when transactional crosses into marketing.