In this Step by Step Guide, I will show you a full SMTP Server Configuration using Postalthe open-source SMTP software, and connect it to your email marketing application to send unlimited emails.

There are several methods to build SMTP servers, in this guide I will build the SMTP server using a free open source software called “Postal“.

Postal is a fully-featured open source mail delivery platform for incoming & outgoing e-mail and gives you all the tools and features needed to build a full mailing system for your business.

What is the SMTP Server?

I don’t like robotic definitions like Wikipedia, I love to make things simple. So…

Simply, SMTP is that thing that allows you to send emails over the internet.

SMTP stands for “Simple Mail Transfer Protocol”. It’s a Concept in Networking that you don’t have to worry about.

Just Know that SMTP is the technical thing that is responsible for delivering emails over the internet.

Let’s connect things, how this is related to email marketing?

I think it’s clear, but just in case, and As I explained in my Techincal Email Marketing guide, any Email marketing system consists of two parts:

  • The sender: (SMTP service) this is the technical part. It allows you to send emails over the internet.
  • The Management Application, where you can configure and manage your Email Lists, Marketing Campaigns, monitor and analyze results, manage your sending servers, and so on.

So we connect both together to get an Email Marketing System.

Email Marketing System

What do we mean by Sending Unlimited Emails?

When we say unlimited emails, this means that we can send unlimited emails from our server, there are no restrictions by companies or monthly plans to buy or so.

It’s your own server, u can send as much your server can handle in terms of resources. so when you have more (CPU and RAM), you can send more emails and so on.

SMTP Server Configuration

Requirements for smtp server configuration.

In order to Build and Setup an SMTP Server, you will mainly need two things:

  1. A Domain name
  2. VPS Server with port 25 opened.

1. Domain name

When you send emails, you will be sending from an email address like this one:

So in my case, “” is the domain name that I use to send my emails. so simply it’s required to have a domain name to use when you send emails from your SMTP server.

Usually, it’s your website domain name, except if you are working with cold emails, then it’s better to get and use another domain in case it got blacklisted, to keep your main business domain safe.

So if you don’t have a domain yet, go and get one NOW! in order to continue the Setup.

How to get a domain? simply you buy one! and it costs around 10$ per year, so it’s not that big deal!

We have a lot of DOMAIN REGISTRATION PROVIDERS where you can get a domain from like:

2. VPS Server with Port 25 opened.

The second thing you will need is a VPS server. a public server to install & Setup SMTP on.

What is a VPS server?

If you don’t know what is a VPS server, simply its a computer (a server) running in the cloud that you buy from a Web Hosting or Cloud Services company. And it’s publicly accessible with a Public IP.

A VPS can be used to host your websites with higher performance, can be used to run a machine 24/7 in the cloud to do any task you want.

Note: If you are interested in learning how to host your own websites on a VPS server, you can

Anyway, In our case, we will be using the VPS Server for smtp server configuration.

Port 25 open??

I mentioned that the VPS must have port 25 opened, what does this mean?

I don’t want to bother your head within deal technical stuff but in short. Any network service or software uses a certain port to communicate over the internet or network. Examples:

  • Connecting remotely to another Windows Machine using RDP software works over port 3389.
  • SQL database systems like MYSQL on our computer works over port 3306.
  • Connecting to a Linux machine remotely to manage it with SSH, uses port 22.
  • When you surf the web and open websites, we use port 80. and so on.

By default, all servers and computers have a firewall running which blocks all ports except the ones you want. so In order to use a certain service, we need to open that port in the firewall.

What you have to know also, that ports can be blocked and opened in two ways, incoming and outgoing, the following diagram will make things clearer:

Inbound and Outbound Ports

I recommend you to watch my free course “Amazon EC2 for Digital Marketers” you will understand all these concepts in less than an hour.

So, in our case, we are building an SMTP server, and the SMTP software or protocol communicates over port 25. so we need to have port 25 opened.

So when you get a VPS server, just make sure that the company allows Port 25 an don’t block it, because some companies do this to protect from spammers.

Port 25 is used to send emails

Here is a list of some companies that allows port 25 by default:

  1. Host wind.
  2. Contabo.
  3. Interserver**
  4. OVH.
  5. Digital Ocean*
  6. AWS (some accounts are blocked)

*Digital Ocean Sometimes block some accounts and restrict port 25, but in general they allow all ports.

**Interserver open port 25 if you buy a spam filter service from them. Contact them first.

Are there any other Companies?? yes, simply you can contact the support of any company you want and ask if they block any ports by default. if not, then perfect, you can go with it.

Feel free to use any VPS company you want, It’s up to you!

You can also sign up on DigitalOcean through the coupon link below to get free 100$ to test everything free.

Digital Ocean Coupon Link

Or Start with Contabo which I think is the cheapest VPS service that you can use, I have 2 servers configured with Contabo.

After you select your VPS company, just create a VPS Server with the following specifications:

  • Ubuntu 18 x64 as your operating system
  • You can start with 1 CPU/2 GB RAM (And resize later).

Got your VPS? Great!  Let’s continue.

VPS Server basic configuration.

Now we have our new Ubuntu VPS server, Let’s prepare it for our smtp server configuration.

Connect to your server, using an SSH client like putty or bitvise.

First, check your hostname:

hostname -f

If you don’t see a form of ANYTING.YOURDOMAIN.COM, then you need to change the hostname using the following command:

 sudo hostname host.domain.tld 

Where the host is anything you want. so in my case, my sample domain for this tutorial is, the command will look like this:

sudo hostname

Map your domain name.

Now we have our VPS server and we set its name. Go to your Domain Provider and map your Domain to your VPS server. simply open DNS management zone and add a new A record like this:

host: server points: YOUR SERVER IP.

Godaddy A record

*server is in my case, you can choose whatever you want for your server name.

Done?  Let’s continue.


SMTP Server Configration PreRequisites

Step 1: Install MariaDB Server

Just like any other application, Postal requires a database to save all the data and configuration inside it. To do this, we will install MariaDB using the below commands.

To do that, run the commands below.

sudo apt update
sudo apt install mariadb-server libmysqlclient-dev

After installing MariaDB, the commands below can be used to stop, start and enable MariaDB service to always start up when the server boots.

sudo systemctl stop mariadb.service
sudo systemctl start mariadb.service
sudo systemctl enable mariadb.service

After that, run the commands below to secure the MariaDB server by creating a root password and disallowing remote root access.

sudo mysql_secure_installation

When prompted, answer the questions below:

  • Socket password: N
  • Enter current password for root (enter for none): Just press the Enter
  • Set a root password? [Y/n]: Y
  • New password: Enter your new password (create a secure one)
  • Re-enter new password: Repeat your new password
  • Remove anonymous users? [Y/n]: Y
  • Disallow root login remotely? [Y/n]: Y
  • Remove test database and access to it? [Y/n]:  Y
  • Reload privilege tables now? [Y/n]:  Y

Restart MariaDB Mysql service

To test if MariaDB is installed, type the command below to logon to MariaDB server

sudo mysql -u root -p

Then type the password you created above to login… if successful, you should see MariaDB welcome message like this:

MariaDB Installed Successfully

Installed DB? Great! 

Step 2: Install Ruby and RabbitMQ

Postal needs Ruby, Erlang and RabbitMQ to work.

Install Ruby, Erlang and RabbitMQ packages on Ubuntu. These are required packages and are not available via Ubuntu default repositories.

To install the latest version of Ruby, you might need to do it from a third-party PPA. Below is how to add the PPA and install Ruby.

sudo apt-get install software-properties-common
sudo apt-add-repository ppa:brightbox/ruby-ng

After that, run the commands below to update Ubuntu packages and install Ruby version 2.3.

sudo apt update
sudo apt install ruby2.3 ruby2.3-dev build-essential

Now that you have installed Ruby, continue below to install RabbitMQ. But first, Erlang is a prerequisite. Install Erlang.

wget -O- | sudo apt-key add -
echo "deb bionic contrib" | sudo tee /etc/apt/sources.list.d/rabbitmq.list
sudo apt-get update
sudo apt-get install erlang
sudo apt-get update
Now install RabbitMQ.
curl -s | sudo bash
sudo apt-get install rabbitmq-server

After installing RabbitMQ, the commands below can be used to stop, start and enable RabbitMQ service to always start up when the server boots.

sudo systemctl stop rabbitmq-server
sudo systemctl start rabbitmq-server
sudo systemctl enable rabbitmq-server

Now it is time to configure RabbitMQ by running below commands.

sudo rabbitmqctl add_vhost /postal
sudo rabbitmqctl add_user postal p0stalpassw0rd
sudo rabbitmqctl set_permissions -p /postal postal "." "." ".*"

Install Node.js & Git

Node JS and GIT are required to run postal properly. Install them using below command.

sudo apt install nodejs
sudo apt install git

SMTP Server Installation

Now all that the prerequisites are installed, it is time for smtp server configuration and installation.

Step 1: Create Database

sudo mysql -u root -p 

CREATE DATABASE postal CHARSET utf8mb4 COLLATE utf8mb4_unicode_ci;

Next, create a database user called postal with new password

CREATE USER 'postal'@'' IDENTIFIED BY 'p0stalpassw0rd';

After that, grant the user full access to the postal user database.

GRANT ALL ON `postal`.* TO `postal`@`` IDENTIFIED BY "p0stalpassw0rd";
GRANT ALL PRIVILEGES ON `postal-%` . * to `postal`@``  IDENTIFIED BY "p0stalpassw0rd"; 

Finally, save your changes and exit.


Step 2: Install Postal Mail Server

Now that your server has everything needed to run Postal Mail Server, continue below to get it installed and configured.

First, create a service account for Postal Mail Server

sudo useradd -r -m -d /opt/postal -s /bin/bash postal

Then, allow Ruby to listen to web calls by running the commands below:

sudo setcap 'cap_net_bind_service=+ep' /usr/bin/ruby2.3

Next, installed required packages.

sudo gem install bundler
sudo gem install procodile
sudo gem install nokogiri -v '1.7.2'

Furthermore, create Postal Mail Server directory, download the latest version and extract it into the directory, then give Postal user access.

sudo mkdir -p /opt/postal/app
sudo wget
sudo tar xvf latest.tgz -C /opt/postal/app
sudo chown -R postal:postal /opt/postal
sudo ln -s /opt/postal/app/bin/postal /usr/bin/postal

Last, install Ruby dependencies and initialize Postal configurations.

postal bundle /opt/postal/vendor/bundle
postal initialize-config
postal initialize

Note: In case you face mimemagic locked error after running the first command, run the below commands then run the repeat above commands and continue:

cd /opt/postal/app
bundle update mimemagic
bundle install
cd ~

Step 3: Make Postal admin User

Now Let’s create a user so we can login and manage out Postal Server through the web interface. Simply run the following command:

postal make-user

And this command will ask you to Enter Your Name, Email, and password. so write it down and press Enter.

Postal is Installed! 

Now run below command to start postal.

sudo -u postal postal start

Then run below command to check the status. All should be running.

sudo -u postal postal status

Step 4: NGINX

To manage Postal Mail Server via its web portal, you must install a web server. Run the commands below to install Nginx.

sudo apt install nginx

Then copy Postal Nginx config to use as its VirtualHost.

sudo cp /opt/postal/app/resource/nginx.cfg /etc/nginx/sites-available/default

Then create a self-signed SSL certificate to use with the portal.

sudo mkdir /etc/nginx/ssl/
sudo openssl req -x509 -newkey rsa:4096 -keyout /etc/nginx/ssl/postal.key -out /etc/nginx/ssl/postal.cert -days 365 -nodes

Answer the prompts on the screen.

Also, we need to edit the default file for NGINX using WINSCP as well.

go to: /etc/nginx/sites-available Directory. Then Open the default file.

Replace with your domain name.

Then restart nginx.

sudo systemctl stop nginx 
sudo systemctl start nginx

Postal SMTP Server Configuration

Now, Open your Internet browser, and navigate to your Server IP URL or Subdomain like this:


You will notics an SSL warning, It’s ok just proceed as you see in the image below:

SSL warning

And then the Postal Login Screen will open, enter your email and password that you created during the setup to login.

Postal Login

And Now, you are inside Postal, click “Add Organization” to add one.

Then Click on Build Mail Server and enter the name, and set it to live mode

Create Postal Mail Server

So Simple. 

Edit Postal config file.

To Edit the Postal Configuration File, we will need to connect to our server using a File manager to make things easy.

So, You can Use WinSCP, a free remote file manager, to connect and edit the files on the server.

Open WinSCP, and Connect to your server using the root credentials. and go to: /opt/postal/config Directory. Then Open the postal.yml file.

Postal yml configuration

Then, right-click and edit the file.

postal domain change

As you can see, just change the example domain with your domain name.

After that, you need to restart postal for the configuration to take effect.

So run this command on your server:

postal restart

Postal Domain Configuration

Now, Click On Domains to add you domain name into Postal

Add Domain in Postal

Enter your Domain name that you want to use to send emails, and Click Create Domain.

Then, Postal will show you the Domain page with the records that you need to configure.

Postal DNS records

So, What you need to do simply, is to copy these records and paste in your DNS Zone. and then your server will be ready to send emails! but what are SPF and DKIM?

Dkim (DomainKeys Identified Mail) :

Let’s Start with DKIM, A DKIM record is also a text record in your DNS that holds a public authentication key. This key will be validated using a private key saved privately inside your server.

All emails will be signed, and this will avoid any alterations and protect your email originality, and this is very important for your server to archive high sending scores.

Watch this video for more info:

Setup Dkim For Postal

What’s nice about Postal, is that DKIM is already configured and the keys are generated, you just need to copy the DKIM record to your DNS Zone.

Postal DKIM record

SPF (Sender Policy Framework):

An SPF record is a TXT record that is added to your Domain DNS Zone and allows you to set the mail servers that are allowed to send emails from your domain.

Messages sent from a server that isn’t included in the SPF record will be marked as spam or rejected.

As an example, you can’t send an email from your own server and set your sending email as “,” you can’t use google’s domain. It indicates that you are trying to spam.

In the same way, you can configure SPF and prevent anyone from using your domain to send emails,  So setting SPF is very important when it comes to making your domain trusted by other mailing providers.

To set up SPF. Open your DNS zone in and add the following record:

v=spf1 a mx ip4:XXX.XXX.XXX.XXX -all

*Replace with your VPS server IP.

Now only your server can send emails from your domain.

If you noticed, Postal will give you an example SPF to copy, and it looks like this:

v=spf1 a mx ~all

This is just an example domain, and you will notice it is already your domain since you changed it in the postal config file to match your domain name. 

Finally! Send a Test Email

Postal has built-in functionality to test sending emails, simply click on Messages, then on Send Message to test out the Free SMTP server!


Optional Smtp Server Configuration: Secure with a Free SSL.

SSL certificates are used within web servers to encrypt the traffic between the server and client, providing extra security for users accessing your application. Let’s Encrypt provides an easy way to obtain and install trusted certificates for free.

Connect to your Server using Putty SSH client. and Let’s Start!

Step 1 — Install the Let’s Encrypt Client

Let’s Encrypt certificates are fetched via client software running on your server. The official client is called Certbot.

Install Certbot by running this command:

apt -y install certbot

Certbot is now ready to be used. 

Step 2 — Get the SSL Certificate

But, before we get an SSL Certificate, we need to stop nginx service since its using port 80 which certbot will use. so Let’s stop it temporarily by running the following comnad:

sudo systemctl stop nginx

Now let’s install the certificate, run the following command:

certbot certonly --standalone -d

Replace “” with your domain.

And follow the wizard. Then certbot will issue a certificate for your domain.

Step 3 — Configure the SSL Certificate

After we got the SSL certificate, we need to configure it in our server.

Let’s start the nginx service again:

sudo systemctl start nginx

Now, Open WinSCP again to edit some files on our server.

Connect to your server, and go to /etc/nginx/conf.d directory.

In this folder, create a new file and name it: “

Replace “” with your domain.

Then, Simply copy the following code and paste inside the file.

server {
    listen [::]:80;
    return 301 https://$host$request_uri;
server {
    listen [::]:443 ssl;
    listen ssl;
    root /opt/postal/public;
    ssl_certificate      /etc/letsencrypt/live/;
    ssl_certificate_key  /etc/letsencrypt/live/;
    ssl_protocols TLSv1.2 TLSv1.1 TLSv1;
    ssl_prefer_server_ciphers on;
    location / {
       client_max_body_size 50M;
       try_files $uri $uri/index.html $uri.html @puma;
    location /app/assets {
       add_header Cache-Control max-age=3600;
    location @puma {
        proxy_set_header X-Real-IP  $remote_addr;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;

And save the file.

The last step is to restart and enable nginx again. Simply run the following command:

systemctl restart nginx

Then this command:

systemctl enable nginx

And Awesome, Now you can test your secure Postal website!

I hope you enjoyed this tutorial for smtp server configuration.

Good Luck!