Hands-off email campaigns that can't double-send
A scheduler fires every 5 min. It checks which campaigns are due, builds the send list, removes duplicates and unsubscribes, and dispatches in batches. No one presses send.
emails sent in the first 3 months: 98.6% delivered, bounced, zero double-sends.
The suppression list is checked at send time, not at list-build time, so someone who unsubscribes between build and send is still protected. This adds one query per batch but removes the class of bug entirely.
- HANDLEDscheduler fires twice
- Each batch carries a unique send key. The email provider rejects a duplicate key, so nobody is emailed twice regardless of how many times the job runs.
- HANDLEDunsubscribe arrives between build and send
- Suppressions are checked at send time, not at list-build time. A contact who opts out minutes before a batch goes out is removed before the batch fires.
- HANDLEDsender domain not verified
- The domain check runs before any send attempt. An unverified domain blocks the campaign entirely rather than letting it fail mid-way.
- RETRYsend stalls mid-batch
- After 30 minutes with no completion, the campaign is marked Failed and surfaced in the dashboard. It is never left half-sent and silent.