Check your existing tools
Both an HTTP API and SMTP can connect an application to an email service. The better starting point depends on how your application is built and how much control you need over requests, responses, and delivery events.
If an existing application or WordPress mail plugin already accepts SMTP settings, SMTP can be a straightforward fit. For a new integration, a structured HTTP API can make it easier to connect email requests to your own application records.
When to use an email API
With an HTTP integration, your application sends an authenticated request and receives a structured response. Keep the API key on your server, use a verified sending domain, and record the request identifiers you need for troubleshooting.
Where the endpoint supports idempotency, use the same idempotency key when retrying the same logical send. Review the documented behavior instead of assuming that every failed network request means the email was never accepted.
Read the API quickstartWhen to use SMTP
SMTP works well with software that already has a mail transport configuration. In SendMailOS, follow the SMTP guide for the correct host, sending password, verified domain, and TLS configuration.
The documented connection options include STARTTLS on port 2525 and implicit TLS on port 2465. Use the settings required by your application and the current guide rather than copying a different provider’s defaults.
Read the SMTP setup guideTrack delivery after the request
An accepted send request and a delivered message are different events. Connect the documented webhooks to follow delivery outcomes, and verify incoming signatures before your application acts on them.
Keep enough context to connect an event with the original request. Handle supported retries safely, and use your workspace and request identifiers when investigating a result. That gives your team a clearer view of email as part of the product.
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