How to Relay Emails to Gmail

Introduction

This tutorial applies to RHEL 8 based operating systems (CentOS, Rocky Linux)

Two machines that send emails are:

• vav.combpio.ucsf.edu
• bksmailman.compbio.ucsf.edu

Relaying emails through gmail will make it more secure and trustworthy.

Instructions

Reference Tutorial

1. Create a gmail account OR Ask Khanh for docking.email@gmail.com for credentials.
2. Disable pre-installed 'sendmail' package

   • rpm -q sendmail (Check for package)
     systemctl disbale sendmail --now (Disable package)

3. Enable smtp in firewall

   • firewall-cmd --permanent --add-service=smtp

4. Install Postfix and other dependencies

   • yum install postfix mailx cyrus-sasl cyrus-sasl-plain -y

5. Configure Postfix

   • vim /etc/postfix/main.cf
     
     //Copy these lines and paste it at the bottom of the main.cf file
     relayhost = [smtp.gmail.com]:587
     smtp_use_tls = yes
     smtp_sasl_auth_enable = yes
     smtp_sasl_security_options = noanonymous
     smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
     smtp_tls_security_level = encrypt
     smtp_tls_CAfile = /etc/ssl/certs/ca-bundle.crt

6. Set up authentication file for gmail

   • vim /etc/postfix/sasl_passwd
     
     //Paste this line and replace
     [smtp.gmail.com]:587 docking.email@gmail.com:<gmail_app_password>

7. Create Gmail App Password For Authentication
   • Log in to gmail account
   • Click top right account button
   • Click 'Manage Google Account'
   • On the left, click the 'Security' tab
   • Enable '2-step Verification'
   • Now back to security tab and click 'App Passwords'
   • Generate App Password
   • Click 'Other' for the category input
   • Copy the generated token and save somewhere
8. Once you have token, replace <gmail_app_password> in sasl_passwd file with the token and save the file
9. Update the password database

   • postmap /etc/postfix/sasl_passwd
     chown root:root /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
     chmod 0600 /etc/postfix/sasl_passwd /etc/postfix/sasl_passwd.db
     systemctl restart postfix.service
     systemctl status postfix

10. Verify that it works

    • echo "This is the body of the email" | mail -s "This is the subject line" <your_email>

11. If it works you're done. If it doesn't check the reference tutorial for troubleshooting.