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How to Send Email in Linux from the Command Line with Sendmail and Mailx

How to Send Email in Linux from the Command Line with Sendmail and Mailx
Awais Khan
Technical writer
Mail Linux
18.03.2025
Reading time: 7 min

For those managing servers or working on automation tasks, knowing how to send emails from the Linux terminal is essential. It offers complete control over email functions and eliminates the need for complex mail programs. This is useful in scenarios where speed and simplicity matter most.

Common tools such as sendmail and mailx are frequently used for sending messages, checking SMTP settings, automating alerts, and integrating with scripts. They are straightforward yet effective, making them perfect for tasks like informing teams about server updates, automating reports, or testing email setups.

This guide is designed for users looking to manage their email directly from the terminal. It covers the installation of essential tools and delves into more advanced tasks, such as sending attachments and configuring email tools.

Why Choose Command-Line Email Tools?

Two commonly used tools, sendmail and mailx, are reliable options for mail transmission in Linux. They come with a certain set of benefits:

  • Efficiency: Traditional email software can be slow and resource-intensive. These tools enable quick and lightweight email sending directly from the terminal.
  • Automation: They integrate smoothly with shell scripts, cron processes, and system monitoring tools. Automating mail alerts and notifications for repeated actions is possible via these Linux mail tools.
  • Troubleshooting SMTP Problems: Debugging SMTP setups becomes more manageable. These commands provide visibility into message delivery, ensuring mail logs and errors are easier to inspect.
  • Flexibility: Whether it’s sending alerts or generating automated reports, command-line tools like sendmail and mailx offer versatility across a range of tasks.

Prerequisites 

Before utilizing these Linux mail command line tools, ensure you have terminal access. Root privileges may be required in some cases, especially for configuring each mail command on Linux discussed in this guide.

Setting Up a SMTP Server

SMTP servers are essential for sending emails. These servers fall into two categories: External and Local SMTP servers.

External SMTP Servers

It refers to a mail server hosted by a third-party provider. These servers are utilized to deliver emails over the internet to recipients who are not part of your local network. They are built to manage global mail delivery while ensuring proper authentication, encryption, and spam prevention.

Examples 

  • Gmail 

Address: smtp.gmail.com

Port: 587 (with TLS) or 465 (with SSL)

  • Outlook 

Address: smtp.office365.com

Port: 587

These servers need appropriate authentication methods (such as a username, password, or app-specific passwords) and encryption (like TLS or SSL) to ensure secure communication.

Note: We’ve already provided a guide for setting up external SMTP servers. The command to send emails through Postfix remains the same as mentioned in this article. Simply configure the SMTP settings using our guide, and replace the email address with Gmail or any other preferred provider for proper email delivery.

Local SMTP Servers

This server functions solely within a private network or system. It is perfect for:

  • Sending emails between users on the same network or domain (e.g., tom@office.local to jerry@office.local).
  • Local testing and development tasks.
  • Internal communication within an organization.
  • Does not need internet access to operate, as they manage mail delivery internally.

Setting Up a Local SMTP Server

Here are the procedures to set up a local SMTP server using Postfix:

  1. Install Postfix via:

sudo apt install postfix
  1. Modify the Postfix configuration file:

sudo nano /etc/postfix/main.cf
  1. Update or confirm these key settings:

myhostname = mail.office.local
mydomain = office.local
myorigin = $mydomain
inet_interfaces = loopback-only
local_recipient_maps = proxy:unix:passwd.byname
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
  1. Save and exit the file after doing changes, then restart Postfix:

sudo systemctl restart postfix
  1. To create email addresses like linux@office.local and hostman@office.local, set up user accounts on the server:

sudo adduser linux
sudo adduser hostman

Overview of sendmail

sendmail is a prominent mail transfer agent (MTA) in Linux. It works flawlessly with SMTP servers for mail delivery and allows emails to be sent and routed from local systems or scripts. 

Installing sendmail 

Before sending emails, you must install the Linux sendmail tool. Execute the commands below based on your distribution:

For Debian/Ubuntu

sudo apt install sendmail

For CentOS/Red Hat

sudo yum install sendmail

Starting and Enabling Service

Once installed, make sure sendmail is running and configured to start at boot:

sudo systemctl start sendmail
sudo systemctl enable sendmail

Testing the Configuration

Check the sendmail is set up correctly by executing:

echo "Testing sendmail setup" | sendmail -v your-email@example.com

Image2

Verify email by executing the mail command:

mail

Image4

Note: Install mailutils package in case the mail command is not working.

sudo apt install mailutils

Or utilize the cat command:

cat /var/mail/user

Image3

Editing the Configuration File

To customize settings for sendmail, modify the configuration file located at /etc/mail/sendmail.mc:

sudo nano /etc/mail/sendmail.mc

Image1

Make the required changes to fit your server. For example, if you want to define the domain name for your server, you can add or modify the following line:

define(`confDOMAIN_NAME', `your_domain.com')dnl

Here, replace your_domain with your actual domain name.

Then rebuild the configuration file:

sudo m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

If a "permission denied" error occurs, use:

sudo sh -c "m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf"

Finally, restart the service:

sudo systemctl restart sendmail

Sending Email Via sendmail

With sendmail, you can easily deliver emails, customize subjects, and even add attachments using external tools. Let’s go over the process to send emails:

Basic Example

To send an email with sendmail, use the below-given instructions:

  1. First, create a file to hold the message:

nano email.txt
  1. Add any content to the file, for example:

Subject: Test Email from Hostman
This is a test email sent using sendmail on Linux.
  1. Deliver the file's contents:

sendmail recipient@example.com < email.txt

The contents of email.txt will be sent to the designated recipient.

Image6

  1. For verification, apply:

mail

Image5

Adding Attachments 

sendmail by itself doesn’t support attachments. You’ll need to utilize uuencode or similar tools to include files. First, install sharutils for uuencode:

sudo apt install sharutils

Here’s how to attach a file:

( echo "Subject: Email with attachment"; uuencode file.txt file.txt ) | sendmail recipient@example.com

In the above sendmail example we send an email with file.txt attached.

Image8

To verify, apply the Linux command mail:

mail

Image7

Overview of mailx 

The mailx Linux command is a simple and effective terminal application for managing emails. It is included in the mailutils package found in most Linux distributions.

Installing mailx 

Install mailutils package on your system to utilize the mailx command on Linux:

For Debian/Ubuntu systems

sudo apt install mailutils

For Red Hat-based systems

sudo yum install mailx

Sending Email with mailx

This is a simple example demonstrating the use of mailx.

  1. Include a subject line and message in your email:

echo "This is the body of the email" | mailx -s "Test Email from Mailx" recipient@example.com

Image11

Utilize the Linux mail command for verification:

Image9

Example with Attachments

Use the -A flag with the mailx command to send emails from Linux with attachments:

echo "Please find the attached document" | mailx -s "Email with Attachment" -A email.txt recipient@example.com

This sends email.txt as an attachment to the recipient.

Image10

Conclusion

Sending email from the Linux command line is an effective method for automating communication tasks, troubleshooting servers, or testing configurations. Using tools such as sendmail and mailx, you can manage everything from simple messages to more complex setups with attachments. This guide has provided detailed instructions to help you begin without difficulty. Utilize these Linux email commands to improve your workflow. If you face any issues, feel free to refer back to this tutorial.

Mail Linux
18.03.2025
Reading time: 7 min

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Step 2: Configuration with an External SMTP Server Set up the relay host and enable security protocols by adding the provided lines to the file: relayhost = [smtp.example.com]:587smtp_sasl_auth_enable = yessmtp_sasl_password_maps = hash:/etc/postfix/sasl_passwdsmtp_sasl_security_options = noanonymoussmtp_tls_security_level = encryptsmtp_tls_note_starttls_offer = yes Here: The initial line configures the Postfix relay host. This line sets the SMTP and port (587 for TLS); if you’re using Gmail, replace "smtp.example.com" with "smtp.gmail.com." The second line enables SASL authentication. The third line points to the file containing your SMTP credentials (an essential file that helps setup Postfix map sasl_password. The fourth line prevents anonymous connections. The fifth line causes the utility to utilize TLS encryption. The sixth line reports the server's STARTTLS offer. Save the file once you’ve adjusted the necessary settings. 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09 December 2024 · 8 min to read
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How to Use Google SMTP Server

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'/vendor/autoload.php'; use PHPMailer\PHPMailer\PHPMailer; use PHPMailer\PHPMailer\SMTP; use PHPMailer\PHPMailer\Exception; $mail = new PHPMailer(true); // Specify that we are using SMTP $mail->isSMTP(); // Enable debugging output for testing purposes $mail->SMTPDebug = 2; $mail->Debugoutput = 'html'; // Provide the SMTP credentials $mail->Host = 'smtp.gmail.com'; // SMTP host $mail->Port = 587; // SMTP port $mail->SMTPSecure = 'tls'; // Encryption $mail->SMTPAuth = true; // Enable authentication $mail->Username = "user@gmail.com"; // Your Google account email $mail->Password = "62584jattjjtmxnpwf124"; // App-specific password // Specify sender and recipient information $mail->setFrom('test-mail@hostman.com', 'Test Sender Hostman); // Sender $mail->addReplyTo('replyto@example.com', 'First Last'); // Reply-To address $mail->addAddress('mail@yahoo.com', 'James Smith'); // Recipient // Subject and content $mail->Subject = 'Hostman: Google SMTP Test'; // Subject line $mail->msgHTML('<h1>Hello, Hostman</h1>'); // HTML content $mail->AltBody = 'This is a plain-text message body'; // Plain-text fallback // Output the result if (!$mail->send()) { echo "Mailer Error:". $mail->ErrorInfo; } else { echo "Message sent!"; } You can use the same script by replacing the credentials and recipients with your own information, including the Reply-To address. 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Let's install Postfix and the postfix-mysql package for database integration: apt install postfix postfix-mysql During installation, select Internet Site when prompted. This assumes you have access to edit DNS records and can specify an FQDN (Fully Qualified Domain Name). In the next window, keep the server name as is and continue. After installation, create a new user account to handle mail operations. First, create a group called vmail using groupadd: addgroup -gid 1080 vmail Next, create the vmail user and assign the home directory to /home/mail: adduser --home /home/mail -gid 1080 -uid 1080 vmail Where 1080 is the group ID (GID) and user ID (UID). If 1080 is already taken, you can choose a different value. Verify that the /home/mail directory belongs to the vmail user and group: ll /home Configuring Postfix With the user created, proceed to configure Postfix by editing the main configuration file /etc/postfix/main.cf: nano /etc/postfix/main.cf Make the following edits: # Domains we accept mail for mydestination = localhost.$mydomain, localhost, localhost.localdomain # Postfix protocol inet_protocols = ipv4 # Path to the public certificate smtpd_tls_cert_file = /etc/ssl/mail/public.pem # Path to the private certificate smtpd_tls_key_file = /etc/ssl/mail/private.key Then, add additional options required for Postfix to function correctly: # Mail storage location virtual_mailbox_base = /home/mail # Path to alias maps virtual_alias_maps = proxy:mysql:/etc/postfix/mysql_virtual_alias_maps.cf # Domain storage format virtual_mailbox_domains = proxy:mysql:/etc/postfix/mysql_virtual_domains_maps.cf # Mailbox storage format virtual_mailbox_maps = proxy:mysql:/etc/postfix/mysql_virtual_mailbox_maps.cf # Minimum virtual user ID virtual_minimum_uid = 1080 # UID for the main user handling mail virtual_uid_maps = static:1080 # GID for the group handling mail virtual_gid_maps = static:1080 # Register Dovecot as the mail delivery agent virtual_transport = dovecot # Enable secure authentication smtpd_sasl_auth_enable = yes smtpd_sasl_exceptions_networks = $mynetworks smtpd_sasl_security_options = noanonymous broken_sasl_auth_clients = yes smtpd_sasl_type = dovecot smtpd_sasl_path = private/auth # Enable TLS encryption for outgoing SMTP connections smtp_use_tls = yes # Enable TLS support for incoming connections smtpd_use_tls = yes smtpd_tls_auth_only = yes smtpd_helo_required = yes Now, create the files referenced in the Postfix configuration. Start with the alias maps: nano /etc/postfix/mysql_virtual_alias_maps.cf Add the following content: user = postfix password = postfixPa$$w0rd hosts = localhost dbname = postfix query = SELECT goto FROM alias WHERE address='%s' AND active = '1' Similarly, configure the domain maps: nano /etc/postfix/mysql_virtual_domains_maps.cf Add: user = postfix password = postfixPa$$w0rd hosts = localhost dbname = postfix query = SELECT domain FROM domain WHERE domain='%u' Finally, configure the mailbox maps: nano /etc/postfix/mysql_virtual_mailbox_maps.cf Add: user = postfix password = postfixPa$$w0rd hosts = localhost dbname = postfix query = SELECT CONCAT(domain,'/',maildir) FROM mailbox WHERE username='%s' AND active = '1' Edit the master.cf file: nano /etc/postfix/master.cf Add the following settings: submission inet n - n - - smtpd -o smtpd_tls_security_level=may -o smtpd_sasl_auth_enable=yes -o smtpd_sasl_type=dovecot -o smtpd_sasl_path=/var/spool/postfix/private/auth -o smtpd_sasl_security_options=noanonymous -o smtpd_sasl_local_domain=$myhostname smtps inet n - n - - smtpd -o syslog_name=postfix/smtps -o smtpd_tls_wrappermode=yes -o smtpd_sasl_auth_enable=yes -o smtpd_client_restrictions=permit_sasl_authenticated,reject dovecot unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/deliver -d ${recipient} Generating Security Certificates To ensure secure email transactions, generate security certificates using openssl. First, create the directory where the certificates will be stored (as specified in the main.cf file): mkdir -p /etc/ssl/mail Generate the certificates: openssl req -new -x509 -days 1000 -nodes -out /etc/ssl/mail/public.pem -keyout /etc/ssl/mail/private.key -subj "/C=CY/ST=Limassol/L=Limassol/O=Global Security/OU=IT Department/CN=mail.devnullhost.com" Finally, enable and restart Postfix: systemctl enable postfix && systemctl restart postfix Installing and Configuring Dovecot Dovecot is an open-source IMAP and POP3 server. We'll install it along with the required modules for database integration: apt install dovecot-imapd dovecot-pop3d dovecot-mysql Next, we configure the mail storage method. Open the Dovecot configuration file: nano /etc/dovecot/conf.d/10-mail.conf In the file, specify the directory structure for storing mail. We'll use a hierarchy of domain → user: mail_location = maildir:/home/mail/%d/%u/ In the same file, configure the authentication method: service auth { unix_listener /var/spool/postfix/private/auth { mode = 0666 user = postfix group = postfix } unix_listener auth-userdb { mode = 0600 user = vmail group = vmail } } service stats { unix_listener stats-reader { user = vmail group = vmail mode = 0660 } unix_listener stats-writer { user = vmail group = vmail mode = 0660 } } Edit the Dovecot authentication configuration file: nano /etc/dovecot/conf.d/10-auth.conf Replace the line !include auth-system.conf.ext with !include auth-sql.conf.ext, indicating that SQL-based authentication should be used. Next, configure SSL encryption in Dovecot: nano /etc/dovecot/conf.d/10-ssl.conf In this file, add the following: ssl = required ssl_cert = </etc/ssl/mail/public.pem ssl_key = </etc/ssl/mail/private.key When users connect for the first time, we want their mailboxes to be automatically created. To enable this, open the following file: nano /etc/dovecot/conf.d/15-lda.conf Add the following line: lda_mailbox_autocreate = yes Now, configure Dovecot to connect to the database. Open the SQL configuration file: nano /etc/dovecot/dovecot-sql.conf.ext Add the following lines to configure MySQL: driver = mysql connect = host=localhost dbname=postfix user=postfix password=postfixPa$$w0rd default_pass_scheme = MD5-CRYPT password_query = SELECT password FROM mailbox WHERE username = '%u' user_query = SELECT maildir, 1080 AS uid, 1080 AS gid FROM mailbox WHERE username = '%u' user_query = SELECT CONCAT('/home/mail/',LCASE(`domain`),'/',LCASE(`maildir`)), 1080 AS uid, 1080 AS gid FROM mailbox WHERE username = '%u' Open the main Dovecot configuration file to set up the server interface: nano /etc/dovecot/dovecot.conf In this file, add the following line to listen on all available network interfaces: listen = * Finally, enable and restart Dovecot to apply the configuration: systemctl enable dovecot && systemctl restart dovecot Installing and Configuring PostfixAdmin For PostfixAdmin to work correctly, you need a configured web server, PHP, and a MySQL database (either a LAMP or LEMP stack). In this guide, we will skip the web server setup and go directly to installing PostfixAdmin. First, install the necessary PHP extensions: apt install php-mysql php-mbstring php-imap Download PostfixAdmin to the web server's root directory using wget: wget https://sourceforge.net/projects/postfixadmin/files/latest/download -O postfixadmin.tar.gz Create a directory for PostfixAdmin and extract the archive contents: mkdir -p /var/www/html/postfixadmin && tar -C /var/www/html/postfixadmin -xvf postfixadmin.tar.gz --strip-components 1 Then, create a directory for storing template caches: mkdir /var/www/html/postfixadmin/templates_c Set the correct permissions for the web server to access the PostfixAdmin directory: chown -R www-data:www-data /var/www/html/postfixadmin Create the database and a user for PostfixAdmin: mysql -u root CREATE DATABASE postfix DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_general_ci; GRANT ALL ON postfix.* TO 'postfix'@'localhost' IDENTIFIED BY 'postfixPa$$w0rd'; exit; In the local configuration file of PostfixAdmin, add the database configuration: nano /var/www/html/postfixadmin/config.local.php The file contents should be: <?php $CONF['configured'] = true; $CONF['default_language'] = 'en'; $CONF['database_password'] = 'postfixPa$$w0rd'; $CONF['emailcheck_resolve_domain']='NO'; ?> Open the PostfixAdmin setup page in your browser by going to /postfixadmin/public/setup.php. You will be prompted to generate a password hash for authentication. Enter the password and click the button. A message containing the hash will appear below the form. Copy this hash and insert it into the config.local.php file: nano /var/www/html/postfixadmin/config.local.php Refresh the /postfixadmin/public/setup.php page and log in with the password you used to generate the hash. If everything is configured correctly, you should see a configuration check page. At the bottom of this page, there is a form to create an admin account. After successfully creating the admin, go to /postfixadmin/public/login.php and log in with the credentials you just set up. You will be redirected to the PostfixAdmin administration panel. Creating a Mailbox in PostfixAdmin In your browser, go to /postfixadmin/public/. In the top menu, choose "Domain List → New Domain." Then, in the "Overview → Create Mailbox" section, enter the details for a test email account. You can now test the connection using email clients. Use the following connection parameters: Server: Your server's hostname IMAP: Port 143, STARTTLS POP3: Port 110, STARTTLS SMTP: Port 25, STARTTLS Login and Password: The credentials you specified when creating the mailbox Conclusion In this guide, we explored what a self-hosted email server is and the technologies and software used to configure it. The main advantage of having your own mail server is the ability to fully customize it: create unlimited mailboxes, assign aliases, and manage users. All these features can be implemented by renting a cloud server from Hostman and configuring the server following this guide.
17 October 2024 · 12 min to read

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