Send mail from scripts and backends with your account API key (shown under User app after you sign in). All JSON bodies use UTF-8.
Include your key on every /sendmail request:
Header: X-API-Key: <your API key>Sending is rejected if your account is not verified, sending is disabled by an admin, or the key is wrong.
Delivers one message. The visible From address is fixed by the server; from_name sets the display name only. html_body is optional (sanitized on the server). The web UI calls POST /api/send with the same JSON fields and your browser session cookie instead of an API key.
Simple liveness check for monitors and load balancers (no auth).