Introduction
REST API for sending email and managing your audience — authentication, endpoints, errors, and guides.
The mailer123 API lets you send transactional email and manage your audience programmatically — everything you can do in the dashboard, over HTTP.
This is a REST API. Requests and responses are JSON over HTTPS. Authenticate
with an API key (a bearer token). The API is versioned in the URL path; the
current version is v1. Every endpoint is relative to your base URL:
text
https://mailer123.com/api/v1At a glance
| Property | Value |
|---|---|
| Protocol | HTTPS only |
| Format | JSON request and response bodies |
| Auth | Bearer API key in the Authorization header |
| Versioning | In the path (/v1). Breaking changes ship as a new version. |
What you can do
- Send email — fire a single transactional message and get a delivery id back.
- Manage contacts — create, read, update, and delete contacts and custom fields.
- Organize groups — create groups, manage members, and add contacts to them.
- Run campaigns — list campaigns and start a draft sending.
- Read templates — fetch reusable email bodies.
- View domains — read a project's sending domains and their verification status.
Next steps
New here? Start with the Quickstart to send your first email in a couple of minutes, then read Authentication. When you're ready to build, jump to the API reference.