MailerSend

Capabilities

These values come from the adapter's exported capabilities declaration. The field support matrix covers normalized message fields.

The MailerSend adapter calls the MailerSend Email API with plain fetch. Two quirks to know: MailerSend accepts exactly one reply-to address, and the message id comes back in the x-message-id response header rather than the body.

MailerSend@opencoredev/email-sdk/mailersend

Provider docs

Configure

Create an API token in the MailerSend dashboard and verify the domain you plan to send from.

import { createEmailClient } from "@opencoredev/email-sdk";
import { mailersend } from "@opencoredev/email-sdk/mailersend";

export const email = createEmailClient({
  adapters: [mailersend({ apiKey: process.env.MAILERSEND_API_KEY! })],
});

Send

MailerSend maps cc, bcc, headers, attachments (an attachment's contentId becomes MailerSend's id), and tags (values only). replyTo accepts a single address; two or more throw an EmailValidationError before any request. sendAt maps to send_at (a Unix timestamp in seconds), so MailerSend holds the message until then. It accepts at most 72 hours in the future.

const result = await email.send({
  from: "Acme <hello@acme.com>",
  to: [{ email: "user@example.com", name: "Ada" }],
  replyTo: "support@acme.com",
  subject: "Reset your Acme password",
  html: "<p>Click the link below to choose a new password.</p>",
  tags: [{ name: "type", value: "password-reset" }],
});

console.log(result.id); // MailerSend message id from the x-message-id header

The response id comes from the x-message-id response header, falling back to message_id or id in the body. Use it to look the send up in MailerSend's activity log.

Verify from the CLI

MAILERSEND_API_KEY="mlsn..." npx email-sdk doctor --adapter mailersend

MAILERSEND_API_KEY="mlsn..." npx email-sdk send \
  --adapter mailersend \
  --from "Acme <hello@acme.com>" \
  --to user@example.com \
  --subject "MailerSend smoke test" \
  --text "It works" \
  --dry-run

Drop --dry-run for one real send. The token, domain verification, and plan limits only prove themselves against the live API.

Compare MailerSend with other providers

Side-by-side message-field support from the SDK capability matrix, with working code for both adapters:

• Resend vs MailerSend
• Brevo vs MailerSend