How to Setup SMTP Relay: A Step-by-Step Guide

Published October 7, 2024 · Updated July 6, 2026 · Guides & Tutorials

Setting up an SMTP relay does not have to be intimidating. Whether you are wiring up an app, a website, or a bulk mailer, the process follows the same clear path. This step-by-step guide takes you from zero to a working, authenticated SMTP relay that lands in the inbox.

Step 1: Choose your relay

Decide between a shared relay (cheap, shared reputation) and a dedicated SMTP relay (your own IP, best deliverability). For anything that matters, dedicated is worth it.

Step 2: Get your connection details

Your provider gives you four things: host, port (587), username, and password. These are what every app or device will use to connect.

Step 3: Authenticate your domain

Publish SPF, DKIM, and DMARC DNS records for your sending domain. This is the step that decides inbox versus spam — a managed relay generates these for you.

Step 4: Configure your sender

Enter the host, port 587, STARTTLS, username, and password into your app, mailer, or script. Set the "from" address to your authenticated domain.

Step 5: Test and warm up

Send a test to yourself and confirm it lands in the inbox with authentication passing. Then warm up your sending volume gradually before going full-scale.

The one that trips people up: Step 3. A relay that connects and "sends" can still land in spam if SPF/DKIM/DMARC are not passing. Verify authentication before you trust it with real mail.

Steps 1–3 done for you

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Frequently asked questions

How do I set up an SMTP relay step by step?

Choose a relay, get your host/port/username/password, authenticate your domain with SPF/DKIM/DMARC, configure your sender on port 587, then test and warm up.

What port should the relay use?

Port 587 with STARTTLS for authenticated submission. Avoid port 25, which is often blocked and less secure.

How long does setup take?

With a managed dedicated SMTP, minutes — the server, IP, and authentication are ready on signup. Self-configuring your own DNS adds a little time for records to propagate.