Sendmail relay configuration

The joys of sendmail relay configuration!

Sendmail is a popular open-source mail transfer agent (MTA) that can be configured to relay email messages to other mail servers. Here's a step-by-step guide to help you configure sendmail relay:

Prerequisites:

1. Sendmail is installed and running on your system.
2. You have a mail server (MTA) that you want to relay email messages to.

Step 1: Edit the sendmail.cf file

The sendmail.cf file is the main configuration file for sendmail. You'll need to edit this file to configure the relay settings.

1. Open the sendmail.cf file in a text editor: sudo nano /etc/sendmail.cf (or the equivalent path on your system).
2. Add the following lines at the end of the file:

   # Relay settings
   define(`RELAY_HOST', `your.mail.server.com')  # Replace with your mail server's hostname
   define(`RELAY_PORT', `25')  # Replace with your mail server's SMTP port
   define(`RELAY_USER', `your.mail.server.username')  # Replace with your mail server's username
   define(`RELAY_PASSWORD', `your.mail.server.password')  # Replace with your mail server's password

   Replace your.mail.server.com, your.mail.server.username, and your.mail.server.password with the actual values for your mail server.

Step 2: Edit the sendmail.mc file

The sendmail.mc file is a macro file that is used to generate the sendmail.cf file. You'll need to edit this file to include the relay settings.

1. Open the sendmail.mc file in a text editor: sudo nano /etc/mail/sendmail.mc (or the equivalent path on your system).
2. Add the following lines at the end of the file:

   FEATURE(`authinfo', `hash -o /etc/mail/authinfo')dnl
   define(`RELAY_HOST', `your.mail.server.com')dnl
   define(`RELAY_PORT', `25')dnl
   define(`RELAY_USER', `your.mail.server.username')dnl
   define(`RELAY_PASSWORD', `your.mail.server.password')dnl

   Replace your.mail.server.com, your.mail.server.username, and your.mail.server.password with the actual values for your mail server.

Step 3: Generate the sendmail.cf file

1. Run the following command to generate the sendmail.cf file from the sendmail.mc file:

   sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

   Step 4: Restart sendmail

2. Restart the sendmail service to apply the changes:

   sudo service sendmail restart

   Step 5: Test the relay

3. Send a test email from your system to a recipient outside your network to verify that the relay is working correctly.

That's it! With these steps, you should now have sendmail configured to relay email messages to your mail server.