Find out why the Mailgun send reached nobody else

Why did that email only reach you?

The sandbox rule, usually, and a companion checks it in the right order: list the domains on the account, open the one you are sending from, and say plainly whether it is verified or a sandbox with an authorised-recipients list. Thirty seconds of reading that saves the morning.

The send tool is the most complete of the email integrations in this set. It takes a verified sending domain, a from address inside it, recipients with cc and bcc, an HTML or text body, a tracking flag for opens and clicks, a delivery time for scheduled sending, and per-recipient variables for personalisation. If your transactional mail needs a bcc to an archive address, this one carries it.

What does the event log actually answer?

More than a dashboard glance does.

The event query takes a domain and a time window in RFC 2822 format, returns up to three hundred events a page with cursor paging, and covers accepted, delivered, opened and failed. Point a companion at a bad afternoon and it walks every page rather than reading the first screen and stopping, which is the difference between "some failures around 2 p.m." and "every message to one recipient domain failed between 14:05 and 14:40".

Statistics come from a separate tool that returns totals for a domain over a window, bucketed by day by default. The series tells you whether this week is worse than last; the event log tells you which messages made it worse. A companion reads both and writes the paragraph you act on.

Then it keeps going. Once the log names the failing recipient domain, the same companion opens that company's postmaster page, checks whether your sending IP appears on a public blocklist, and reads your own status page for a coinciding deploy. That is the ordinary research move, applied to an incident.

• "Every failed event for this domain between Friday 09:00 and Friday 18:00, grouped by recipient domain."
• "Compare delivered and failed totals for the last two weeks, day by day."

Keep mailing list membership honest

The integration covers mailing lists properly: create a list inside a verified domain, list the lists, page through the members filtered by subscribed or unsubscribed, add a member with a display name and custom variables, and remove one. The add call has an upsert flag, and it earns its place: without it, re-adding an existing member is an error, and a companion working through forty addresses would stop dead on the third. Forty addresses, one pass, ordinary operations work.

Alert in Mailgun, investigate in the browser

Webhooks push events the moment they happen and keep working while everyone is asleep.

The investigation that follows the alert is the companion’s half, and it is the half that takes a person an hour: walk the event log, group the failures, name the recipient domain, and check what shipped at the same moment.

Domain setup stays in Mailgun, where DNS verification decides whether the mail is deliverable at all, and the integration reads domains rather than creating them. One setting to choose: the send is not on the browser's always-interrupt list, so switch the profile to Ask Always in Settings → AI permissions for a guaranteed pause before anything leaves.

Frequently asked questions