SMTP Quickstart

This guide configures the Mailtarget SMTP relay and verifies one delivery from your terminal. About five minutes if your sending domain is verified.

Connection settings​

Host:       smtp.mtrgt.net
Port:       587
Encryption: STARTTLS
Username:   smtp_mt_injection
Password:   <api_key with Send via SMTP permission>

The username is fixed for every account. The password is your API key. Create the key in the dashboard and grant it the Send via SMTP permission. Read Authentication for permission scope details.

Quick verification with swaks​

swaks is the standard tool for verifying SMTP from a terminal. Install it with your package manager (brew install swaks on macOS, apt install swaks on Debian or Ubuntu).

swaks \
  --to recipient@example.com \
  --from you@your-verified-domain.com \
  --server smtp.mtrgt.net:587 \
  --tls \
  --auth LOGIN \
  --auth-user smtp_mt_injection \
  --auth-password "$MAILTARGET_API_KEY" \
  --header "Subject: SMTP test from Mailtarget" \
  --body "If you can read this, the relay works."

A successful run ends with the relay returning a 250 Ok status and a queued message ID.

Configuring an existing application​

Most applications expose the same five fields. Map them to the values above.

Postfix​

relayhost = [smtp.mtrgt.net]:587
smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = encrypt

The sasl_passwd file contains:

[smtp.mtrgt.net]:587 smtp_mt_injection:<api_key>

Run postmap /etc/postfix/sasl_passwd and systemctl reload postfix after writing the file.

WordPress (WP Mail SMTP plugin)​

In WP Mail SMTP, Settings, choose Other SMTP and enter:

• SMTP Host: smtp.mtrgt.net
• SMTP Port: 587
• Encryption: TLS (the plugin uses "TLS" to mean STARTTLS on port 587)
• Authentication: enabled
• SMTP Username: smtp_mt_injection
• SMTP Password: your API key

Java (Spring Boot)​

spring:
  mail:
    host: smtp.mtrgt.net
    port: 587
    username: smtp_mt_injection
    password: ${MAILTARGET_API_KEY}
    properties:
      mail.smtp.auth: true
      mail.smtp.starttls.enable: true
      mail.smtp.starttls.required: true

Node.js (Nodemailer)​

import nodemailer from "nodemailer";

const transport = nodemailer.createTransport({
  host:   "smtp.mtrgt.net",
  port:   587,
  secure: false,        // STARTTLS, not implicit TLS
  requireTLS: true,
  auth: {
    user: "smtp_mt_injection",
    pass: process.env.MAILTARGET_API_KEY,
  },
});

await transport.sendMail({
  from:    '"Your Name" <you@your-verified-domain.com>',
  to:      "recipient@example.com",
  subject: "SMTP test from Mailtarget",
  text:    "If you can read this, the relay works.",
});

Common SMTP errors​

For the full error catalog including SMTP response codes, read Errors and Rate Limits.

What is next​

The SMTP relay accepts the message at submit time, but the final delivery state arrives via webhook. Wire Webhooks before going to production. Without webhooks, you have no way to detect bounces, complaints, or unsubscribes.

If you decide later that you want server-side templates, structured metadata, or per-recipient substitution data, switch to the API path. Read API vs SMTP for the comparison and API Quickstart for the migration.