Home
Contact salesLog in
Release notes

SMTP Relay Now Available for Email API

27, Oct 2026

Telnyx Email API customers can now send email over standard SMTP: point any existing mail system at smtp.telnyx.com and route email through Telnyx alongside API sends.

What's new

  • Standard SMTP support: Mail servers, frameworks, and legacy apps send through Telnyx with a host, port, and credential change. STARTTLS required, with AUTH PLAIN or AUTH LOGIN using your API v2 key.
  • One platform for API and SMTP: SMTP submissions flow through the same pipeline as API sends: same verified domains, same quotas and billing, same detail records and webhooks.
  • Telnyx message ID in the 250 reply: Correlation and support tooling work unchanged.
  • Messages up to 25 MB: The relay advertises SIZE 25000000 in EHLO and accepts messages up to that limit.
  • Wire-verified protocol contract: Every reply string, timeout, and limit is published, including clean 552 rejections for oversized messages.
  • Provider migration guides: Translation tables for 13 SMTP providers (SendGrid, Mailgun, SES, Postmark, and more), framework configurations, and a cut-over playbook.

Why it matters

Most email infrastructure already speaks SMTP, which makes this the shortest path onto the platform. Apps that have sent mail for years can switch providers with a config change instead of a bespoke connector. And because SMTP rides the same pipeline as the API, one platform covers domains, quotas, billing, and events instead of stitching another vendor into the stack.

Example use cases

  • Teams running legacy applications and mail servers that can only send through SMTP.
  • WordPress, Django, and Rails apps configured through framework mail settings.
  • Organizations consolidating email with voice and messaging on Telnyx.

Getting started

  1. Point your mail system at smtp.telnyx.com on port 587 with STARTTLS enabled.
  2. Authenticate with the username apikey and your Telnyx API v2 key as the password.
  3. Send from a verified sending domain on your account.
  4. Use the message ID from the 250 acceptance reply to match webhooks and Email Detail Records.
const nodemailer = require("nodemailer");

const transport = nodemailer.createTransport({
  host: "smtp.telnyx.com",
  port: 587,
  secure: false,     // 587 uses STARTTLS; 465 is not offered
  requireTLS: true,  // upgrade or abort
  auth: {
    user: "apikey",  // literal string
    pass: process.env.TELNYX_API_KEY,
  },
});

Learn more in the SMTP Protocol Contract, the SMTP Migration Guides, and the Send Email API reference.