Send transactional email with CloudMailin Outbound

CloudMailin also provides an Outbound transactional service. An incoming address and HTTP target do not automatically supply the outbound domain, credentials, or bounce configuration.

Prepare outgoing delivery

1. Follow Outbound getting started and publish the domain-specific bounce/SPF and DKIM instructions.
2. Obtain the actual SMTP/API connection details from the account dashboard.
3. Use a maintained client, authenticate securely, and require the documented STARTTLS/TLS behavior for SMTP.
4. Submit one approved message from the verified identity to a controlled recipient.

Do not copy example bounce-subdomain CNAME values from another domain. Preserve the From/header identity and envelope/bounce-domain distinction in your configuration.

Correlate acceptance and feedback

For SMTP, retain the provider message identifier returned on acceptance. The outbound guide documents bounce feedback containing an events array with fields such as kind, recipient, and message_id; handle each authenticated event separately.

Persist the application send intent and delivery evidence, tolerate duplicate callbacks, and avoid automatic resend after an uncertain timeout. A successfully accepted message is not proof of final inbox placement.

CloudMailin Outbound is for transactional traffic. Do not convert it into a campaign transport simply because an application can submit multiple messages. MailKite is a separate SDK/receiving contract; provider IDs and credentials cannot be interchanged during migration.