Configuring Postfix for Relay

In Part 1, we covered the prerequisites for integrating Postfix with Office 365. Now, we’ll dive into the configuration steps necessary to set up Postfix as an email relay for Office 365. This guide will help you route outbound emails through Office 365, ensuring reliable email delivery.

  1. Configuring Postfix for Relay
    1. Step 1: Update Postfix Configuration
      1. Step 2: Configure SMTP Authentication
      2. Step 3: Set Up Additional Security (Optional)
      3. Step 4: Restart Postfix
      4. Step 5: Verify Postfix Configuration
    2. Step 6: Test the Configuration
    3. Conclusion

Step 1: Update Postfix Configuration

The main configuration file for Postfix is located at /etc/postfix/main.cf. You will need to modify this file to set up Postfix for relaying through Office 365.

  • Open the Configuration File:
sudo nano /etc/postfix/main.cf
  • Modify or Add the Following Settings:
# Specify the hostname of your mail server
myhostname = mail.yourdomain.com

# Replace with your domain
mydomain = yourdomain.com

# Define the local networks
mynetworks = 127.0.0.0/8

# Specify the relayhost as Office 365
relayhost = [smtp.office365.com]:587

# Enable SMTP Authentication
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_type = simple
smtp_use_tls = yes

# Set TLS security options
smtp_tls_security_level = may
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

Step 2: Configure SMTP Authentication

To authenticate Postfix with Office 365, you need to create a password file that stores your Office 365 credentials.

  • Create the SASL Password File:

sudo nano /etc/postfix/sasl_passwd

  • Add Your Office 365 Credentials: Use the following format, replacing username@yourdomain.com and yourpassword with your actual Office 365 username and password:
[smtp.office365.com]:587 username@yourdomain.com:yourpassword
  • Secure the Password File:Change the permissions of the sasl_passwd file to ensure it’s secure
sudo chmod 600 /etc/postfix/sasl_passwd
  • Create the Postfix Hash Database:Generate the hash database file for Postfix to read:
sudo postmap /etc/postfix/sasl_passwd

Step 3: Set Up Additional Security (Optional)

For improved security, consider using an app password if you have multi-factor authentication (MFA) enabled on your Office 365 account. You can generate an app password from your Microsoft account settings.

Step 4: Restart Postfix

After making the necessary changes, restart the Postfix service to apply the new configuration:

sudo systemctl restart postfix

Step 5: Verify Postfix Configuration

You can check the status of Postfix to ensure it’s running properly:

sudo systemctl status postfix

Additionally, you can view the mail log to see if there are any errors or issues:

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

Step 6: Test the Configuration

To verify that your Postfix setup can successfully relay emails through Office 365, perform the following test:

  • Send a Test Email:Use the mail command to send a test email. If you don’t have the mail utility installed, you can install it with:

sudo apt install mailutils

Then send a test email

echo "This is a test email from Postfix." | mail -s "Test Email" recipient@example.com

  • Check the Recipient’s Inbox:Verify that the email has been received in the recipient’s inbox.
  • Review Mail Logs:If the email doesn’t arrive, check the mail logs for any error messages:

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

Conclusion

In Part 2 of this series, we configured Postfix to relay emails through Office 365. You learned how to set up SMTP authentication and tested the configuration to ensure successful email delivery.

In the next part, we’ll discuss troubleshooting common issues that may arise during this process and provide solutions to ensure a seamless integration between Postfix and Office 365.

Stay tuned for Part 3, where we will address troubleshooting techniques!