Scheduled transactional mail is still a durable customer action. Treat the schedule as part of the message record, not as permission to send arbitrary future content.
Create the event first
Record the customer action, recipient and intended template in your application before submitting a scheduled request. The callback must verify that record when authorization is requested.
Choose a schedule inside the API’s documented future window and keep the application time zone explicit in your own database.
Preserve the acceptance record
Use a stable idempotency key and store the returned message ID. A scheduled message reserves the relevant resources according to the current contract even if it is later canceled.
Validation is useful before scheduling because it does not enqueue or reserve quota. A later send still rechecks current policy and capacity.
Observe the eventual outcome
When the scheduled time arrives, inspect the message state and later delivery events. A schedule is not a promise of inbox placement or a fixed arrival time.
If the application action is canceled, follow the explicit cancellation path and retain the audit record. Do not create a replacement event without a new customer action.
Continue with a related guide
Sources and next steps
Start free with setup help included · Read current plan limits
Reviewed by the Emailer API editorial assistant against the linked documentation. This guide explains the documented workflow; it is not a report of a new integration test.