HowTo Install & Config Postfix on Ubuntu 22.04
From: https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-on-ubuntu-22-04 




How To Install and Configure Postfix

on Ubuntu 22.04

Published on April 25, 2022
By Mark Drake and Jamon Camisso

How To Install and Configure Postfix on Ubuntu 22.04





Introduction


Postfix is a popular open-source Mail Transfer Agent (MTA) that can be used to 
route and deliver email on a Linux system. It is estimated that around 25% of 
public mail servers on the internet run Postfix.

In this guide, you’ll learn how to install and configure Postfix on an Ubuntu 
22.04 server. Then, you’ll test that Postfix is able to correctly route mail by
installing s-nail, a Mail User Agent (MUA), also known as an email client.

Note that the goal of this tutorial is to help you get Postfix up and running 
quickly with only some bare-bones email functionality. You won’t have a full 
featured email server by the end of this guide, but you will have some of the 
foundational components of such a setup to help you get started.





Prerequisites


Setting up and maintaining your own mail server is complicated and 
time-consuming. For most users, it’s more practical to instead rely on a paid 
mail service. If you’re considering running your own mail server, we encourage 
you to review this article on why you may not want to do so.

If you’re sure you want to follow this guide to install and configure Postfix, 
then you must first have the following:


Note that this tutorial assumes that you are configuring a host that has the 
FQDN of mail.example.com. Wherever necessary, be sure to change example.com or 
mail.example.com to reflect your own FQDN.





Step 1 — Installing Postfix


Postfix is included in Ubuntu’s default repositories, so you can install it with
APT.

To begin, update your local apt package cache:

	sudo apt update

Then install the postfix package with the following command. Note that here we 
pass the DEBIAN_PRIORITY=low environmental variable into this installation 
command. This will cause the installation process to prompt you to configure 
some additional options:

	sudo DEBIAN_PRIORITY=low apt install postfix

This installation process will open a series of interactive prompts. For the 
purposes of this tutorial, use the following information to fill in your prompts:

To be explicit, these are the settings used in this guide:


Note: If you need to ever return to change these settings, you can do so by typing:

	sudo dpkg-reconfigure postfix

The prompts will be pre-populated with your previous responses.  

When you are prompted to restart services, accept the defaults and choose OK.

When the installation process finishes, you’re ready to make a few updates to your Postfix configuration.





Step 2 — Changing the Postfix Configuration


Now you can adjust some settings that the package installation process didn’t 
prompt you for. Many of Postfix’s configuration settings are defined in the 
/etc/postfix/main.cf file. Rather than editing this file directly, you can use 
Postfix’s postconf command to query or set configuration settings.

To begin, set the location for your non-root Ubuntu user’s mailbox. In this 
guide, we’ll use the Maildir format, which separates messages into individual 
files that are then moved between directories based on user action. The 
alternative option that isn’t covered in this guide is the mbox format, which 
stores all messages within a single file.

Set the home_mailbox variable to Maildir/. Later, you will create a directory 
structure under that name within your user’s home directory. Configure 
home_mailbox by typing:

	sudo postconf -e 'home_mailbox= Maildir/'

Next, set the location of the virtual_alias_maps table, which maps arbitrary 
email accounts to Linux system accounts. Run the following command, which maps 
the table location to a hash database file named /etc/postfix/virtual:

	sudo postconf -e 'virtual_alias_maps= hash:/etc/postfix/virtual'

Now that you’ve defined the location of the virtual maps file in your main.cf 
file, you can create the file itself and begin mapping email accounts to user 
accounts on your Linux system. Create the file with your preferred text editor;
in this example, we’ll use nano:

	sudo nano /etc/postfix/virtual

List any addresses that you wish to accept email for, followed by a whitespace 
and the Linux user you’d like that mail delivered to.

For example, if you would like to accept email at contact@example.com and 
admin@example.com and would like to have those emails delivered to the sammy 

Linux user, you could set up your file like this:

	/etc/postfix/virtual
contact@example.com sammy
admin@example.com sammy

After you’ve mapped all of the addresses to the appropriate server accounts, 
save and close the file. If you used nano, do this by pressing CTRL + X, Y, then
ENTER.

Apply the mapping by typing:

	sudo postmap /etc/postfix/virtual

Restart the Postfix process to be sure that all of your changes have been 
applied:

	sudo systemctl restart postfix

Assuming you followed the prerequisite Initial Server Setup guide, you will have
configured a firewall with UFW. This firewall will block external connections to
services on your server by default unless those connections are explicitly 
allowed, so you’ll have to add a firewall rule to allow an exception for Postfix.

You can allow connections to the service by typing:

	sudo ufw allow Postfix

With that, Postfix is configured and ready to accept external connections. 
However, you aren’t yet ready to test it out with a mail client. Before you can
install a client and use it to interact with the mail being delivered to your 
server, you’ll need to make a few changes to your Ubuntu server’s setup.





Step 3 — Installing the Mail Client and Initializing the Maildir Structure


In order to interact with the mail being delivered, this step will walk you 
through the process of installing the s-nail package. This is a feature-rich 
variant of the BSD xmail client which can handle the Maildir format correctly.

Before installing the client, though, it would be prudent to make sure your MAIL
environment variable is set correctly. s-nail will look for this variable to 
figure out where to find mail for your user.

To ensure that the MAIL variable is set regardless of how you access your 
account — whether through ssh, su, su -, or sudo, for example — you’ll need to 
set the variable in the /etc/bash.bashrc file and add it to a file within 
/etc/profile.d to make sure it is set for all users by default.

To add the variable to these files, type:

	echo 'export MAIL=~/Maildir' 
	| sudo tee -a /etc/bash.bashrc | sudo tee -a /etc/profile.d/mail.sh

To read the variable into your current session, source the /etc/profile.d/mail.sh file:

	source /etc/profile.d/mail.sh

With that complete, install the s-nail email client with APT:

	sudo apt install s-nail

Before running the client, there are a few settings you need to adjust. Open the
/etc/s-nail.rc file in your editor:

	sudo nano /etc/s-nail.rc

At the bottom of the file, add the following options:

	/etc/s-nail.rc
. . .
set emptystart
set folder=Maildir
set record=+sent 

Here’s what these lines do:


Save and close the file when you are finished. You’re now ready to initialize 
your system’s Maildir structure.

A quick way to create the Maildir structure within your home directory is to 
send yourself an email with the s-nail command. Because the sent file will only
be available once the Maildir is created, you should disable writing to it for 
this initial email. Do this by passing the -Snorecord option.

Send the email by piping a string to the s-nail command. Adjust the command to 
mark your Linux user as the recipient:

	echo 'init' | s-nail -s 'init' -Snorecord sammy

	Note: You may get the following response:

	Output
Can't canonicalize "/home/sammy/Maildir"

This is normal and may only appear when sending this first message.


You can can check to make sure the directory was created by looking for your 
~/Maildir directory:

	ls -R ~/Maildir

You will see the directory structure has been created and that a new message 
file is in the ~/Maildir/new directory:

	Output
/home/sammy/Maildir/:
cur  new  tmp

/home/sammy/Maildir/cur:

/home/sammy/Maildir/new:
1650294586.Vfc01I7e11dM993645.mail.example.com

/home/sammy/Maildir/tmp: 

Now that the directory structure has been created, you’re ready to test out the
s-nail client by viewing the init message you sent and sending a message to an 
external email address.





Step 4 — Testing the Client


To open the client, run the s-nail command:

	s-nail

In your console, you’ll see a rudimentary inbox with the init message waiting:

	Output
s-nail version v14.9.15.  Type `?' for help
"/home/sammy/Maildir": 1 message 1 new
>N  1 sammy@example.com     2022-04-18 15:09   14/452   init

Press ENTER to display the message:

	Output
[-- Message  1 -- 14 lines, 452 bytes --]:
Date: Mon, 18 Apr 2022 15:09:46 +0000
To: sammy@example.com
Subject: init
Message-Id: <20220418150946.EE6897E11A@@mail.example.com>
From: sammy@example.com

init 

You can get back to the message list by typing h, and then ENTER:

	?   h

	Output
>R  1 sammy@example.com     2022-04-18 15:09   14/452   init

Notice that the message now has a state of R, indicating that it’s been read.

Since this message isn’t very useful, you can delete it by pressing d, and then ENTER:

	? d

To get back to the terminal, type q and then ENTER:

	? q

As a final test, check whether s-nail is able to correctly send email messages.
To do this, you can pipe the contents of a text file into the s-nail process, 
like you did with the init message you sent in the previous step.

Begin by writing a test message in a text editor:

	nano ~/test_message

Inside, enter some text you’d like to send:

	
~/test_message

Hello,

This is a test.  Please confirm receipt!


Save and close the file after writing your message.

Then, use the cat command to pipe the message to the s-nail process. You can do
so with the following example, which uses these options:

Also, be sure to change user@email.com to a valid email address which you have 
access to:

	cat ~/test_message | s-nail -s 'Test email subject line' -r contact@example.com user@email.com


Then, navigate to the inbox for the email address to which you sent the message. You will see your message waiting there almost immediately.

	Note: If the message isn’t in your inbox, it may have been delivered to your 
Spam folder.


You can view your sent messages within your s-nail client. Start the interactive client again:

	s-nail

From the email client, view your sent messages by typing:

	file +sent

You’ll see output like this:

	Output
+[/home/sammy/Maildir/]sent: 1 message 1 new
▸N  1 To contact@example.com 2022-04-18 15:12   10/211   Test email subject line
You can manage sent mail using the same commands you use for incoming mail.





Conclusion


You now have Postfix configured on your Ubuntu 22.04 server. Managing email 
servers can be a tough task for new system administrators, but with this 
configuration, you should have enough MTA email functionality to get yourself 
started.