Config postfix with gmail to send email from linux command line

A working example on how to config postfix with gmail smtp server to send email directly from linux command line and tested on vagrant vm with ubuntu precise 32.

Install necessary packages

$ sudo apt-get install postfix mailutils libsasl2-2 ca-certificates libsasl2-modules

Open postfix config file /etc/postfix/ and add below content

relayhost = []:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_use_tls = yes

Open /etc/postfix/sasl_passwd and add below line

=> USERNAME: your gmail username
=> PASSWORD: your gmail password or app password if 2-factor authentication is enabled

Set permission and update postfix config to use the sasl_passwd file

$ sudo chmod 400 /etc/postfix/sasl_passwd
$ sudo postmap /etc/postfix/sasl_passwd

Validate certificate

$ cat /etc/ssl/certs/Thawte_Premium_Server_CA.pem | sudo tee -a /etc/postfix/cacert.pem

Start postfix and reload the config

sudo /etc/init.d/postfix start
sudo /etc/init.d/postfix reload
sudo /etc/init.d/postfix restart

Finally send a test email

$ echo "Test mail from postfix" | mail -s "Test Postfix"
=> The echo message is the mail body
=> The -s message is the subject
=> The mail address at the end is the recipient