Email is often a critical component notification for jobs and other things in linux. This is how I set up Postfix on most of my instances. This guide is geared towards Debian based distros but can be translated for others.
Required Software
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sudo apt install postfix mailutils -y
Both Postfix and mailutils make this much easier
Configuration
Open the Postfix configuration file:
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sudo nano /etc/postfix/main.cf
Append the following to the end:
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relayhost = [smtp.gmail.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/gmail_credentials
smtp_sasl_security_options = noanonymous
smtp_use_tls = yes
Notice that instead of adding your gmail credentials directly, we’re adding them to a file named gmail_credentials. Your credentials will depend on whether you use multi-factor authentication (MFA/2FA) or not. If you are now, then you can just put your credentials directly into this file, otherwise you’ll need to create an app password. It is highly recommended to use multi-factor authentication whenever possible so I’ll assume you are.
It is highly recommended to use multi-factor authentication whenever possible
Go to your Google account page and select Security from the side navigation. Then in the center, select 2-Step Verification. After verifying it’s really you, scroll to the bottom and find App Passwords. From this page you can generate a new app specific password. I often select custom from the drop down and give it a descriptive name, then select Generate.
Remember to copy the generated password, because you will never see it again. Now you can use this new generated password instead of your actual password in your gmail_credentials file.
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sudo nano /etc/postfix/gmail_credentials
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[smtp.gmail.com]:587 <username>@gmail.com:<password>
Once you have your credentials file created, you need to secure it add enroll it with postfix.
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sudo chmod 400 /etc/postfix/gmail_credentials
sudo postmap /etc/postfix/gmail_credentials
Now you can reload the Postfix service
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sudo systemctl reload postfix
Testing
Once reloaded, you should be able to send email from the CLI
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echo "This is a test email" | mail -s "Test of Postfix using Gmail" <your@email.address>