The author voluntarily contributed this tutorial as a part of Pepipost Write to Contribute program.

Introduction

In this tutorial, you will learn how to send emails from a Linux operating system's terminal or shell script using popular CLI tools.

This tutorial will help you send critical server-level emails, such as Cron reports, script logs, customer registrations, receipts, and bank statements. 

With simple libraries and very few configurations, you can have a CLI tool in your Linux OS that you can use to send mail from the terminal.

Prerequisites

• Linux operating system
• SMTP Configurations (SMTP server details and authentication credentials)
• Your favorite editor (Optional)
• Configure Gmail SMTP/ready with any other custom SMTP server details. This tutorial talks about using Gmail SMTP to send emails.
• Google SMTP server configurations would look something like this:
• SMTP Server/Hostname: smtp.gmail.com
• SMTP Username: [Your Gmail Address]
• SMTP password: [Your Gmail Password]
• SMTP Port: 587
• TLS/SSL: Required

It's time to open the terminal

Here’s how you use sSMTP to send emails from your Linux command line:  sSMTP is a lightweight utility that allows users to send emails from the command line or shell scripts. This makes it particularly useful for headless servers or cloud platforms without a full mail server installation.

How to install sSMTP to send mails from your Linux command line (CLI)

Step 1

Use the below command to install ssmtp:

sudo apt-get install ssmtp

Optional:
CentOS users can use the below command to install ssmtp:

sudo yum install ssmtp

In CentOS, you may encounter the error "package sSMTP is not available" during installation. To resolve this issue, use the following command:

sudo yum --enablerepo=extras install epel-release

Step 2

After successfully installing sSMTP, configure the global settings as given below to enable mail sending. Open the specified file using your favorite editor, such as nano or vi:

sudo vim /etc/ssmtp/ssmtp.conf

Use the Gmail SMTP server to update the above file with the following details.

mailhub=smtp.gmail.com:587
useSTARTTLS=YES
AuthUser=username-here
AuthPass=password-here
TLS_CA_File=/etc/pki/tls/certs/ca-bundle.crt

To use a third-party SMTP, enter its hostname as the mail hub parameter. For instance, if you want to use Netcore Email SMTP instead of smtp.gmail.com, enter smtp.pepipost.com.

mailhub: your smtp server host/ip with port.

UseSTARTTLS: Set it to Yes if the SMTP server uses TLS or else No.

AuthUser: Use Gmail ID 

AuthPass: Use Gmail ID’s password

TLS_CA_File: This may be required sometimes if you face an issue like ‘send-mail: Cannot open smtp.gmail.com:587’

You are now prepared to send emails using the command line (CLI).

Step 3

There are various methods to use the sSMTP command to send emails.

Case 1: Send Mail Directly From The Command Line

Copy and paste the command below to send an email from your command line.

echo "Test message from Linux server using ssmtp" | sudo ssmtp -vvv [email protected]

-vvv is the verbosity to see the logs while sending the mail

Case 2: Send Mail From A Shell Script

You can also use sSMTP to send mail from a shell script. To do this, open your preferred editor and create a shell script file called 'saymail.sh' and copy and paste the following code:

#!/bin/sh  
SUBJECT="Test Subject"
TO="[email protected]"
MESSAGE="Hey There! This is a test mail"

echo $MESSAGE | sudo ssmtp -vvv $TO

Ensure proper permission access is set for your script file. Use this command to set permission:

$ sudo chmod 755 mail.sh 

Now, execute the code by running the shell script with the following command:

$ sudo ./mail.sh

Here are some common errors/exceptions you may encounter when sending mail with sSMTP:

Error 1

You may encounter the below error message while attempting to send an email:

sSMTP: Authorization failed (535 5.7.8 https://support.google.com/mail/?p=BadCredentials u65smyez14952a76922r5pfui.104 - gsmtp)

[<-] 220 smtp.gmail.com ESMTP u65sm14952769pfu.104 - gsmtp
[->] EHLO kali
[<-] 250 SMTPUTF8
[->] STARTTLS
[<-] 220 2.0.0 Ready to start TLS
[->] EHLO kali
[<-] 250 SMTPUTF8
[->] AUTH LOGIN
[<-] 334 VXNlcm5edhbAWU6
[->] dmlzaGFsY2hhasd2dWhhbjIyMTJAZ21haWwuY29t
[<-] 334 EUEeGFzc3dvfcaqQ6
[<-] 535 5.7.8  https://support.google.com/mail/?p=BadCredentials u65smyez14952a76922r5pfui.104 - gsmtp
ssmtp: Authorization failed (535 5.7.8  https://support.google.com/mail/?p=BadCredentials u65smyez14952a76922r5pfui.104 - gsmtp)
crazy@kali:~/Documents/Scripts$ 

In such case, try the following solutions: 

1. Enable ‘Allow less secure app’ in Google account settings. 

2. Verify correct login credentials. 

3. Run the shell script again for successful output.

$ sudo ./mail.sh

Output:

[<-] 220 smtp.gmail.com ESMTP h8sm1096aae22880pfo.64 - gsmtp
[->] EHLO kali
[<-] 250 SMTPUTF8
[->] STARTTLS
[<-] 220 2.0.0 Ready to start TLS
[->] EHLO kali
[<-] 250 SMTPUTF8
[->] AUTH LOGIN
[<-] 334 VXNlcm5edhbAWU6
[->] dmlzaGFsY2hhasd2dWhhbjIyMTJAZ21haWwuY29t
[<-] 334 UGFzqc3dmvcmQ36
[<-] 235 2.7.0 Accepted
[->] MAIL FROM:<root@kali>
[<-] 250 2.1.0 OK h8smqer10962480pfo.64 - gsmtp
[->] RCPT TO:<[email protected]>
[<-] 250 2.1.5 OK h8smqer10962480pfo.64 - gsmtp
[->] DATA
[<-] 354  Go ahead h8sm10962880pfo.64 - gsmtp
[->] Received: by kali (sSMTP sendmail emulation); Thu, 19 Sep 2019 21:45:14 +0530
[->] From: "root" <root@kali>
[->] Date: Thu, 19 Sep 2019 21:45:14 +0530
[->] Hey There! This is a test mail
[->] 
[->] .
[<-] 250 2.0.0 OK  1568909725 h8smqer10962480pfo.64 - gsmtp
[->] QUIT
[<-] 221 2.0.0 closing connection h8smqer10962480pfo.64 - gsmtp

To sum up, sSMTP is a useful tool for sending emails from the Linux command line. It is particularly helpful for headless servers or cloud platforms that do not have a full mail server setup. By following the above steps l, you can send important server-level emails with ease, from installation to configuration and sending. 

We are a community of email enthusiasts. If you have further queries, feel free to drop an email to [email protected] , and we would be happy to help you.

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