Answer by Sid for How to send mail from the command line?

1. Install ssmtp :

   sudo apt-get install ssmtp
   

2. Edit the ssmtp config file:

   gksu gedit /etc/ssmtp/ssmtp.conf
   

3. Append the following text:

   root=username@gmail.com
   mailhub=smtp.gmail.com:465
   rewriteDomain=gmail.com
   AuthUser=username
   AuthPass=password
   FromLineOverride=YES
   UseTLS=YES
   

4. Run ssmtp and provide the recipient email address:

   ssmtp recepient_name@gmail.com
   

5. Provide the message details as follows:

   To: recipient_name@gmail.com
   From: username@gmail.com
   Subject: Sent from a terminal!
   
   Your content goes here. Lorem ipsum dolor sit amet, consectetur adipisicing.
   (Notice the blank space between the subject and the body.)
   

6. Press Ctrl + D to send.

You can also put the text in file and send it as follows:

ssmtp recipient_name@gmail.com < filename.txt