## Handle unsubscribe in transactional mail
1. Include the `{{{RESEND_UNSUBSCRIBE_URL}}}` placeholder in marketing and product-update mail so every recipient gets a working one-click unsubscribe. Resend replaces it with the real link at send time. Docs: https://resend.com/docs/dashboard/broadcasts/send-broadcast-with-api
2. Decide per email type whether it is transactional or marketing before you write the footer. Receipts, password resets, and security alerts are transactional and must still reach the user; newsletters and promos are marketing and must honor unsubscribes.
3. For mail that sits in the middle, like onboarding tips, add an unsubscribe link even though you could argue it is transactional. The spam-folder cost of a complaint dwarfs the cost of one lost subscriber. Docs: https://resend.com/docs/knowledge-base/should-i-add-an-unsubscribe-link
4. Scope unsubscribes by topic where you can. A user who unsubscribes from the newsletter should keep receiving product announcements unless they opt out of those too; contact topics give you that granularity.
5. Never implement unsubscribe by deleting the contact. Deleting loses the opt-out record, and a re-imported address starts receiving mail again. Update the contact or the topic preference instead.
6. When a marketing unsubscribe arrives, also check the suppression list state. An unsubscribe stops your broadcasts; a complaint or bounce stops everything at the Resend level. Your code must respect both.
7. Test the footer in staging by sending to yourself and clicking through. A placeholder that renders literally in the received mail means the send path did not process it, and real users will see the raw text.