Software⏱️ 4 min read📅 2026-06-11

How to Fix: Postfix error: Host or domain name not found

Postfix error: Host or domain name not found on Raspbian with smarthost configuration.

Quick Answer: Check the Postfix configuration and ensure that the hostname is set correctly after Wi-Fi connection.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🔧 Proven Troubleshooting Steps
  3. 💡 Conclusion

Postfix error: Host or domain name not found is an issue that affects users who are trying to send emails using Postfix on Raspbian. This error occurs when Postfix cannot resolve the host or domain name of the mail server, resulting in emails being stuck in the queue. The frustration comes from the fact that restarting the service temporarily resolves the issue, but it's not a reliable solution and can be inconvenient for users who need to send emails frequently.

This guide aims to help you identify and resolve the root cause of this error, providing two primary fix methods: updating the Postfix configuration and modifying the system's network settings. By following these steps, you should be able to send emails successfully without any issues.

🔍 Why This Happens

  • The first main reason why this error happens is that Postfix is run before the Wi-Fi is connected. When Postfix starts up, it tries to resolve the host or domain name of the mail server using DNS. However, if the system's network settings are not yet configured, Postfix cannot find the correct IP address for the mail server, resulting in the error.
  • Another possible reason for this error is that the Postfix configuration was set to 'Internet with smarthost' during installation, but later modified to 'Internet Site'. This mismatch between the installed and configured settings can cause Postfix to fail when trying to resolve the host or domain name of the mail server.

🔧 Proven Troubleshooting Steps

Update Postfix Configuration

  1. Step 1: Edit the Postfix main.cf file by running the command `sudo nano /etc/postfix/main.cf`.
  2. Step 2: Search for the line that starts with `smtp_smarthost=` and update it to point to the correct mail server IP address. For example, if you're using Gmail's SMTP server, the line should look like this: `smtp_smarthost=smtp.gmail.com:587`. Save and close the file.
  3. Step 3: Restart Postfix by running the command `sudo service postfix restart`.

Modify System Network Settings

  1. Step 1: Check if the system's network settings are configured correctly. You can do this by running the command `ip route show`. Make sure that the Wi-Fi interface is enabled and has an IP address assigned to it.
  2. Step 2: If the Wi-Fi interface is not yet connected, wait for it to establish a connection before sending emails. This should ensure that Postfix runs after the network settings are fully configured.

💡 Conclusion

To summarize, the error 'Host or domain name not found' can be resolved by updating the Postfix configuration or modifying the system's network settings. By following one of these two methods, you should be able to send emails successfully without any issues. Remember to restart Postfix after making any changes to ensure that the new configuration takes effect.

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