--- title: 'Using MXroute as a Relay' url: 'https://kaleb.au/blog/using-mxroute-as-a-relay' markdown: 'https://kaleb.au/blog/using-mxroute-as-a-relay.md' date: '2025-10-07' description: "Running your own mail server with Mailcow is powerful, but outbound deliverability can be challenging - especially if you're on a residential connection, a cloud provider with restricted port 25, or an IP range with a poor reputation. Using MXroute as an SMTP relay (smarthost) is a simple and relia…" --- # [Using MXroute as a Relay](https://kaleb.au/blog/using-mxroute-as-a-relay) 7 Oct 2025 Running your own mail server with **Mailcow** is powerful, but outbound deliverability can be challenging - especially if you're on a residential connection, a cloud provider with restricted port 25, or an IP range with a poor reputation. Using **MXroute** as an SMTP relay (smarthost) is a simple and reliable way to improve delivery while keeping full control of your Mailcow environment. In this post, we'll walk through configuring MXroute as a relay for Mailcow step-by-step. --- ## Why Use MXroute as a Relay? There are a few common reasons to relay outbound mail through MXroute: - Your ISP blocks outbound port **25** - Your server IP has poor reputation or is new - You want better deliverability without managing IP warm-up - You run Mailcow in a home lab or small VPS - You want redundancy for outbound mail - One less thing to deal with MXroute handles the heavy lifting of reputation and delivery, while Mailcow continues to manage users, mailboxes, spam filtering, and inbound mail. --- ## Architecture Overview ```text User / App | v Mailcow (Postfix) | v MXroute SMTP Relay | v Recipient Mail Server ``` Mailcow remains your primary mail server. MXroute is only used for outbound delivery. --- ## Prerequisites Before starting, make sure you have: - A working **Mailcow** installation - An active **MXroute** account - SMTP credentials from MXroute - Outbound connectivity to the MXroute SMTP server (usually port 587) You will need: - SMTP server hostname - SMTP username - SMTP password - SMTP port (typically **587**) --- ## Step 1: Get Your MXroute SMTP Credentials Log into your MXroute control panel and locate: - **SMTP Server** - Example: ```text fusion.mxrouting.net ``` - **Username** ```text user@yourdomain.com ``` - **Password** - **Port** ```text 587 ``` You will use these values in the Mailcow configuration. --- ## Step 2: Configure Mailcow to Use a Relay Host Mailcow uses Postfix internally. The easiest way to configure a relay is by setting environment variables in: ```text mailcow.conf ``` Add or update the following: ```text RELAYHOST=mail.yourdomain.com RELAYHOST_PORT=587 RELAYHOST_USER=user@yourdomain.com RELAYHOST_PASSWORD=yourpassword ``` If these variables already exist, just update them. --- ## Step 3: Apply the Configuration From your Mailcow directory: ```text docker compose down docker compose up -d ``` Or if you want a lighter restart: ```text docker compose restart postfix-mailcow ``` Mailcow will regenerate the Postfix configuration automatically. --- ## Step 4: Verify the Relay is Active Run: ```text docker compose exec postfix-mailcow postconf relayhost ``` Expected output: ```text relayhost = [mail.yourdomain.com]:587 ``` You can also check logs: ```text docker compose logs -f postfix-mailcow ``` Look for lines showing authentication to the relay. --- ## Step 5: Send a Test Email Send a message from: - Mailcow webmail - SMTP client - Application using your Mailcow server Then verify delivery in the logs: ```text status=sent relay=mail.yourdomain.com ``` If you see the MXroute server listed as the relay target, the configuration is working. --- ## Optional: Restrict Relay Usage by Sender Domain In some setups, you may want only specific domains to use the relay. This can be done with Postfix sender-dependent relay configuration, but for most Mailcow deployments, a global relay is sufficient and simpler to maintain. --- ## Troubleshooting ### Authentication Failed Check: - Username - Password - Port - TLS requirement Most MXroute relays require: ```text STARTTLS Port 587 Authentication enabled ``` --- ### Mail Still Sending Directly Common causes: - Mailcow not restarted - Environment variables not set correctly - Typo in hostname - Docker container not reloaded Run: ```text postconf relayhost ``` inside the container to confirm. --- ### TLS Errors If you see certificate errors: - Verify system time - Ensure outbound firewall allows TLS - Check DNS resolution --- ## Security Notes - Always use **port 587 with STARTTLS** - Do not expose SMTP credentials publicly - Rotate passwords periodically - Restrict firewall access to Mailcow if possible --- ## When This Setup Makes Sense Using MXroute as a relay is especially useful when: - Running Mailcow at home - Hosting on small VPS providers - Avoiding IP reputation management - Sending transactional or low-volume mail - Needing reliable outbound delivery quickly --- ## Final Thoughts Relaying outbound mail through MXroute gives you the best of both worlds: - Full control of your mail stack with Mailcow - Reliable delivery infrastructure from MXroute It's a practical setup for homelabs, small infrastructure, and production services where managing mail reputation isn't worth the operational overhead. Simple, reliable, and production-friendly. --- ## Navigation - Parent: [Blog](https://kaleb.au/blog.md) - Previous: [Building Bare-Metal .NET: Exploring NativeAOT Patching](https://kaleb.au/blog/building-bare-metal-net-exploring-nativeaot-patching.md) - Next: [A FOSS Manifesto](https://kaleb.au/blog/a-foss-manifesto.md)