External Checks

As an additional service, we offer you the option to have your mailcow installation checked externally for various aspects.

Info

As of August 2025, we currently only offer an external Open Relay Check. Additional checks are planned.

Open Relay Check

The Open Relay Check verifies whether your mailcow installation acts as an open relay. Open relays pose a significant security risk as they can be exploited by spammers. This can damage your reputation and lead to your IP address being blacklisted if countermeasures are not taken in time.

The check is integrated into the watchdog-mailcow container and is only performed after prior consent (opt-in). Details on activation can be found in the section Activate External Checks.

How It Works

The watchdog container initiates the check by starting an external SMTP connection attempt from our check service. It tries to send an email from an external sender through your server:

• Successful delivery: An open relay is present and should be urgently fixed.
• Failed delivery: Your mailcow installation is correctly configured.

The result is communicated (if configured) via email or webhook.

Performance Note

To reduce system load, the result of the last check is cached. After a correction, it may take some time for an updated result to be available.

Activating External Checks

To activate external checks, the following steps are required:

1. Purchase mailcow SAL: Through the Servercow Customer Portal.
2. Register mailcow: The SAL must be linked to the mailcow as described in the guide Register a mailcow.
3. Adjust configuration: Set the value WATCHDOG_EXTERNAL_CHECKS to y in the mailcow.conf and restart mailcow (docker compose up -d).