Introduction

In Part 2, we successfully configured Postfix to relay emails through Office 365. However, you may encounter some issues during this process. This guide will help you troubleshoot common problems, ensuring a smooth integration of Postfix with Office 365.

  1. Introduction
    1. Common Issues and Solutions
      1. 1. Emails Not Being Delivered
      2. 2. Connection Refused or Timeout Errors
      3. 3. Authentication Failed Errors
      4. 4. SPF Failures
      5. 5. Emails Stuck in Queue
    2. Useful Commands for Troubleshooting
    3. Conclusion

Common Issues and Solutions

1. Emails Not Being Delivered

Symptoms: Emails sent through Postfix are not reaching the recipient’s inbox, or they are bouncing back.

Solutions:

  • Check Mail Logs: The first step in troubleshooting email delivery issues is to check the mail logs. Use the following command to view logs:

sudo tail -f /var/log/mail.log

Look for any error messages or status codes that indicate delivery failures.

  • Verify DNS Settings: Ensure that your DNS records are correctly set up. Check your MX records and SPF records to confirm that they point to Office 365.
  • Confirm Relay Settings: Double-check the relayhost setting in your Postfix configuration (/etc/postfix/main.cf). It should be set to [smtp.office365.com]:587.
  • Test SMTP Authentication: Ensure that your Office 365 credentials in the sasl_passwd file are correct. If you’re using an app password for an account with MFA, confirm that it’s properly entered.

2. Connection Refused or Timeout Errors

Symptoms: You see error messages like “Connection refused” or “Connection timed out.”

Solutions:

  • Firewall Settings: Verify that your firewall allows outbound connections on port 587. You can check this with:

sudo ufw status

  • If the port is blocked, allow it with:

sudo ufw allow 587/tcp

  • Verify Network Connectivity: Test connectivity to the Office 365 SMTP server:

telnet smtp.office365.com 587

If you cannot establish a connection, there may be network issues or restrictions preventing access.

3. Authentication Failed Errors

Symptoms: You receive error messages indicating that authentication has failed.

Solutions:

  • Recheck Credentials: Make sure the username and password in the sasl_passwd file are correct. If using an app password, verify that it is correctly entered.
  • Correct Permissions: Ensure that the permissions on the sasl_passwd file are set correctly.

sudo chmod 600 /etc/postfix/sasl_passwd

After making changes to the password file, remember to regenerate the hash database with:

sudo postmap /etc/postfix/sasl_passwd

  • TLS Configuration: Ensure that you have the proper TLS settings in your Postfix configuration. The following settings should be present in

smtp_use_tls = yes
smtp_tls_security_level = may
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

4. SPF Failures

Symptoms: Recipients report that emails are being marked as spam or not delivered.

Solutions:

  • Check SPF Record: Ensure that your SPF record includes Office 365. A correct SPF record might look like this:

v=spf1 include:spf.protection.outlook.com -all

  • Test SPF: Use online SPF testing tools to check if your SPF record is set up correctly.

5. Emails Stuck in Queue

Symptoms: Emails are not being sent, and you notice a backlog in the Postfix queue.

Solutions:

  • Inspect the Mail Queue: Check the mail queue for pending emails:

mailq

You can use postsuper -d <queue_id> to delete stuck emails if necessary.

  • Examine the Logs: Review the logs to identify why the emails are stuck. Look for specific error messages that can guide your troubleshooting efforts.

Useful Commands for Troubleshooting

  • Check Postfix Status: sudo systemctl status postfix
  • Force Mail Delivery: sudo postfix flush
  • View Mail Logs: sudo tail -f /var/log/mail.log

Conclusion

In Part 3 of this series, we addressed common issues that may arise when configuring Postfix to relay emails through Office 365 and provided solutions to troubleshoot these problems.

In the next part, we’ll explore advanced configurations and optimizations to enhance the performance and security of your Postfix setup. Stay tuned for Part 4, where we’ll take your Postfix and Office 365 integration to the next level!