It is common to send emails using web interfaces like Gmail, Outlook, or Yahoo. However, it is also possible to send emails via the command line. In this blog, we will learn how to send emails using the command line on Linux-based systems. The steps are straightforward and easy to follow.

What You Need

  • A Linux OS
  • Postfix installed
  • Mailutils installed

Step 1: Download the Necessary Tools

Start by installing the required tools on your Linux machine.

Tip: Ask ChatGPT for corresponding commands if you are using a Linux distribution other than Debian-based Linux.

Install Postfix

Postfix is the mail server we will use for sending emails. To install it on a Debian-based Linux system, run the following command:

  sudo apt install postfix

During installation, choose Internet Site as the configuration option.

settings_postfix

Tip: If your system doesn’t find the repository, update it first with sudo apt update

Install Mailutils

Mailutils provides the mail command that we will use to send emails. Install it with:

  sudo apt install mailutils

Check Postfix Installation

Ensure Postfix is installed and running by checking its status:

  systemctl status postfix

If Postfix is disabled, enable it by running:

  sudo systemctl start postfix

Step 2: Test Email Sending

To test if everything is working, you can send an email to a temporary email address (e.g., from Temp Mail).

Use the following command to send a simple email:

  echo "This is a test email content" | mail -a "From: Test <[email protected]>" -s "Put the subject here" [email protected]

Note: This method will not work with email providers like Gmail or Outlook because they often block untrusted mail servers. Use Temp Mail for testing.

Step 3: Bypass Email Filtering

To send emails to services like Gmail or Outlook, you need to use a trusted mail relay SMTP server. The command from last step will be filtered, because systems like Gmail and Outlook are very secure. Here’s how to set up SMTP relay server in postfix:

Obtain SMTP Relay Credentials

Find a third-party email relay service that provides SMTP credentials. This is an example:

Install SASL Authentication Modules

SASL (Simple Authentication and Security Layer) is a protocol used to add authentication support to communication protocols, like SMTP, ensuring secure email transmission.

Install the required modules for SASL authentication:

  sudo apt install libsasl2-modules

Configure SASL with SMTP Relay Credentials

  1. Create the file /etc/postfix/sasl/sasl_passwd and add your SMTP server credentials:

      smtp.server.test:587 [email protected]:password

  2. Generate a hash database file:

      sudo postmap /etc/postfix/sasl/sasl_passwd

    This will create a database file at /etc/postfix/sasl/sasl_passwd.db.

  3. Protect the credentials by setting the correct permissions:

      sudo chown root:root /etc/postfix/sasl/sasl_passwd /etc/postfix/sasl/sasl_passwd.db
sudo chmod 0600 /etc/postfix/sasl/sasl_passwd /etc/postfix/sasl/sasl_passwd.db

Update Postfix Configuration

Edit the Postfix configuration file /etc/postfix/main.cf and update the following settings:

  mydestination = $myhostname, localhost, localhost.localdomain
relayhost = [smtp.server.test]:587
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128

Add these lines to enable SASL authentication:

  # Enable SASL authentication
smtp_sasl_auth_enable = yes
smtp_sasl_security_options = noanonymous
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd
smtp_tls_security_level = encrypt
smtp_tls_CAfile = /etc/ssl/certs/ca-certificates.crt

Restart Postfix

Apply the changes by restarting Postfix:

  sudo systemctl restart postfix

Test if it’s working

You can test if the SASL authentication is working by running:

  echo "This is a test email content" | mail -a "From: Test <[email protected]>" -s "Put the subject here" [email protected]

Note: If the recipient’s mail server is not secure enough, the sender can choose any email they want and spoof that email address. Report such security issues to the system owner to resolve them.

Conclusion

You have now set up email sending from the Linux command line using Postfix and Mailutils. For trusted delivery, configure Postfix to use a reliable SMTP relay service. This approach is powerful but should be used responsibly, especially to avoid unethical practices like email spoofing.