Sending email via Gmail relay through postfix

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There is newer article at CentOS 8.x postfix send email through relay or smarthost with smtp authentication

Avoid use of less secure apps. Better option is to enable 2-step verification. Then create app passwords for apps that do not support 2-step verification / OAUTH etc.. See

Also note that Gmail is likely to stop support for less secure apps very soon (See ). Most of emails sent via gmail using this technique neither seem to get delivered neither bounce back!!!.

To send email via Gmail relay through postfix use:

  1. Configure gmail to use less secure apps using:
    1. Login into Gmail account and go to Settings -> Accounts -> Google Account Settings
    2. In "Google Account Settings" go to Sign-in and Security.
    3. In Sign-in and security change "Allow less secure apps:" to ON
  2. yum -y install cyrus-sasl cyrus-sasl-plain cyrus-sasl-lib postfix mailx
  3. Note that without cyrus-sasl and related packages error no worthy mechanisms found would be received while authenticating to Gmail via postfix. Refer
  4. Set at least following in /etc/postfix/ for mail system to work properly:
    inet_interfaces = all
    inet_protocols = ipv4
  5. edit /etc/postfix/sasl_passwd and put something like <gmail-email-address>:<gmail-password>
  6. Create hash postmap of sasl_password using:
    cd /etc/postfix
    chmod 600 sasl_passwd
    postmap hash:/etc/postfix/sasl_passwd
  7. edit /etc/postfix/ and after relayhost comment lines insert
    smtp_sasl_auth_enable = yes
    smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
    smtp_sasl_security_options =
    smtp_tls_security_level = may
    relayhost =
  8. service postfix restart
  9. echo "Test email using postfix" | mail -s "Gmail relay test"
  10. Look for successful email being sent or errors logs using:
    tail -50 /var/log/maillog
    Logging into above configured "Less secure Gmail" account via browser also helps

To troubleshoot look at /var/log/maillog. In log lines look at value of ctladdr such as 'ctladdr=saurabh (501/501)'. Then look at /var/mail/saurabh or login as user saurabh and use 'mail' command to see error message sent by Gmail server.

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