Send asynchronous email with MailerSend's SDK

Install the documented JavaScript client with npm install mailersend. Supply MAILERSEND_API_KEY, APP_FROM, and TEST_TO through secure backend configuration. Approve the real sender and controlled recipient before running this live send:

import { MailerSend, EmailParams, Sender, Recipient } from "mailersend";
for (const key of ["MAILERSEND_API_KEY", "APP_FROM", "TEST_TO"]) {
  if (!process.env[key]) throw new Error(`Missing ${key}`);
}
const client = new MailerSend({ apiKey: process.env.MAILERSEND_API_KEY });
const message = new EmailParams()
  .setFrom(new Sender(process.env.APP_FROM))
  .setTo([new Recipient(process.env.TEST_TO)])
  .setSubject("MailerSend controlled test")
  .setText("A message from the approved application sender.");
await client.email.send(message);

Retain asynchronous correlation

The sending reference describes asynchronous acceptance and the x-message-id used for subsequent status inspection. Capture that identifier using the response/header access documented for your installed SDK version, and associate it with a previously persisted send intent.

Check provider activity and the controlled inbox before expanding traffic. A 202 acceptance is not a final delivery result. Follow applicable activity/webhook APIs for ongoing feedback instead of an unbounded polling loop.

Validation, permission, or unverified-domain failures need specific fixes. If the connection times out after submission, investigate the message record before repeating it or falling back to another sender. MailKite is a separate transport with its own SDK/domain verification, not a shared bearer-token endpoint.