Test Sending Emails using Sendmail's SMTP Server

Table of Contents

The Case #

I was working on some email sending programs and I needed to test them locally. I found out that there are some tools that can help me with that. One of them is sendmail, which is a popular CLI tool to send emails to Linux users from your command line. You can also use it to send emails globally, but you need to configure it more and do some research. If you are interested, you can look it up.

Real Stuffs #

Use the following commands to install sendmail in a debian/ubuntu environment.

Install these tools
- sendmail for sending mails from command line
- mailutils for viewing/sending mails

apt install sendmail mailutils -y

Configure sendmail’s SMTP Server

sendmailconfig

Send email to the linux user debian from root.

echo "Subject: Hello world" > /tmp/test.txt
sendmail -v debian@localhost < /tmp/test.txt

Check the mailbox

# switch to debian user
$ sudo su debian
# Check mailbox
$ mail

"/var/mail/debian": 5 messages 1 new 2 unread
 U   1 Mail Delivery Subs Sun Aug 13 06:00  72/3052  Returned mail: see tr
 U   2 Mail Delivery Subs Sun Aug 13 10:08  63/2412  Warning: could not se
     3 root               Sun Aug 13 17:19  27/1121
     4 Debian             Sun Aug 13 17:53  14/603
>N   5 Debian             Tue Aug 15 14:35  12/620   Hello world
? 5
Return-Path: <debian@vps-ncbdhsd.vps.ovh.us>
Received: from vps-ncbdhsd.vps.ovh.us (localhost [127.0.0.1])
        by vps-ncbdhsd.vps.ovh.us (8.17.1.9/8.17.1.9/Debian-2) with ESMTP id 37FEZu5U247448
        for <debian@vps-ncbdhsd.vps.ovh.us>; Tue, 15 Aug 2023 14:35:56 GMT
Received: (from root@localhost)
        by vps-ncbdhsd.vps.ovh.us (8.17.1.9/8.17.1.9/Submit) id 37FEZubT247447
        for debian@localhost; Tue, 15 Aug 2023 14:35:56 GMT
Date: Tue, 15 Aug 2023 14:35:56 GMT
From: Debian <debian@vps-ncbdhsd.vps.ovh.us>
Message-Id: <202308151435.37FEZubT247447@vps-ncbdhsd.vps.ovh.us>
Subject: Hello world

That’s it! You’re ready to test your python, nodejs, php, rust or any other apps.