In this Step by Step Guide, I will show you how to set up a Free SMTP server using Postal, the open source SMTP software, and connect it to your email marketing applicaiton to send Unlimited Emails*.

Also, you will find a video below Showing the setup if you feel something is unclear.

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.

postal free smtp server setup
Email Marketing System

So now I think It's SUPER clear, we are going to learn how to build the first part of any email marketing system which the SMTP server.

Need more details?

Maybe you are that person who loves to go deep in topics and understand everything in detail like me 😁 if you are that person, you can watch the following 3 minutes video to learn more about SMTP servers and how it works:

You can find more videos on my YouTube Channel.

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.

Setup the SMTP Server, Let's Start!

Ok, So Let's start the real work! but before, you need to know what is required.

Requirements to Setup SMTP Server.

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:

  • Godaddy.
  • Namecheap.
  • freenom.
  • Enom.
  • Google Domain.

Here in the course, I will be using Godaddy to get my domain, but you can use any other service if you want, all work in the same way, and if you need any help,  I will be here 🙂

You can watch this 3 minutes video to see how to get and buy a domain from Godaddy Domain Registrar if you are a beginner.

This video is part of my Top Rated Course On Udemy:
Build Your Own SMTP and Send Unlimited Emails

Got a Domain? Great! ✔️ Let's continue.

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 Building an SMTP server.

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:

Setup SMTP Server - ports
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.

Setup SMTP Server port 25
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.

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.

Or Start with Contabo which I think its 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 out Setup.

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.

Setup SMTP Server - Godaddy A record
Godaddy A record

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

Done? ✔️ Let's continue.

Setup Free SMTP Server

The VPS is ready, and we can start the installation process. So in order to setup SMTP Server on our VPS, we need to install an SMTP software.

Install Postal Free SMTP Software


Postal runs entirely using containers which means to run Postal you'll need some software to run these containers. We recommend using Docker for this purpose but you can use whatever software you wish.

To install docker, run below commands. (NOTE: Each command starts with a – )

-sudo apt-get update
-sudo apt-get install \
    apt-transport-https \
    ca-certificates \
    curl \
    gnupg \
-curl -fsSL | sudo gpg --dearmor -o /usr/share/keyrings/docker-archive-keyring.gpg
-echo \
  "deb [arch=amd64 signed-by=/usr/share/keyrings/docker-archive-keyring.gpg] \
  $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
-sudo apt-get update
-sudo apt-get install docker-ce docker-ce-cli
-sudo curl -L "$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose
-sudo chmod +x /usr/local/bin/docker-compose
-docker-compose --version

System utilties

There are a few system utilities that you need to have installed before you'll be able to run some of the Postal commands.

apt install git curl jq

Git & installation helper repository

Make sure you have git installed on the server by running below commands.

-git clone /opt/postal/install
-sudo ln -s /opt/postal/install/bin/postal /usr/bin/postal

Maria DB

You can run MariaDB in a container, assuming you have Docker, using this command. Copy and paste this all in Putty.

docker run -d \
   --name postal-mariadb \
   -p \
   --restart always \
   -e MARIADB_DATABASE=postal \

This will install your postal database on MariaDB.


RabbitMQ is responsible for dispatching messages between different processes. As with MariaDB, there are numerous ways for you to install this. For this guide, we're just going to run a single RabbitMQ worker. Copy all the below as one command and paste on putty.

docker run -d \
   --name postal-rabbitmq \
   -p \
   --restart always \


Run the command below and replace with the actual hostname you want to access your Postal web interface at. Make sure you have set up this domain with your DNS provider before continuing.

postal bootstrap postal.YOURDOMAIN.COM

Initializing the database

Run the following commands to create the schema and then create your first admin user.

postal initialize
postal make-user

Running postal

You're now ready to run Postal. You can do this by running:

postal start

This will run a number of containers on your machine. You can use postal status to see details of these components.

Installing WEB Client

You can use any web client to run postal on your web, but in this guide, we are going to use Caddy. Install it with an SSL using below command.

docker run -d \
   --name postal-caddy \
   --restart always \
   --network host \
   -v /opt/postal/config/Caddyfile:/etc/caddy/Caddyfile \
   -v /opt/postal/caddy-data:/data \

Once this has started, Caddy will issue an SSL certificate for your domain and you'll be able to immediately access the Postal web interface and login with the user you created in one of the previous steps.

Configure Postal SMTP

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
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
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

postal free smtp server setup
Create Postal Mail Server

So Simple. ✔️

Postal Domain Configuration

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

Add Domain in 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
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
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 need to change this in the postal config file to match your domain name. How?

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
Postal yml configuration

Then, right-click and edit the file.

postal domain change
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

And Refresh your web page, you must see now that was replaced by your domain and you can simply copy the SPF record to your DNS zone.

postal spf record
Postal SPF record

Very Nice! ✔️

Now our Server is ready for testing.

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 Free SMTP server!

Send a test message


Now you may be wondering how to use this SMTP as a relay to send emails from any email marketing application.

The Answer is simply by creating “Credentials” inside Postal to connect and authenticate to our Free SMTP Server.

Create Postal Credentials to Relay Emails

To create credentials, simply click on Credentials, then Add new Credentials.

For the Type, Select SMTP.

You can also select API if you wanna connect to postal through the API or develop your own application that works with Postal. Read more about the API here.

Enter a User (Anything you want)

And the Key, is the password, you can keep it as “automatically generated

postal free smtp credentials

And that's it, you can now use these credentials in any email marketing application.

Relay a Test Email

Simple, Go to SMTPER.NET and enter your server details as follows:

Test your SMTP
  • SMTP Host: Your Server IP or Domain.
  • Port: 25 or 2525
  • Login: The User You entered in credentials.
  • Password: The User Password.

So, these are the credentials that you can use in any Email Sender Application.

That's it! I hope everything was simple and clear. we finish setting up the Free SMTP Server!

If you have any problems, you can open your questions on

And if you like to get the Full Udemy Course On Build Your Own Cold Email Outreach System – Postal & Mautic, you can enroll now with a Special Limited Time Discount.

Check Also: PowerMTA Mail Server Full Setup Guide 👈

Before You Send!

Congratulations! You Setup your own Free SMTP Server using Postal. but before you start sending emails, you have to understand some crucial concepts and follow up on the guidelines to get the best delivery rates and reach the inbox!

Warming Up your SMTP server

When you build a New SMTP Server with a new IP Address, and Before You can Start Sending Your Email Marketing Campaigns, you have to warm up your IP Address.

What is Warming Up IP?

When you have a new Brand IP Address for your SMTP, this IP will have no Reputation on the internet, and ISPs (internet service providers) don't know this IP.

So IP warmup is the practice of building Your Reputation on The Internet by gradually increasing the volume of mail sent with your IP address according to a predetermined schedule.

Example of warming up your server shown in the table below:

Warmup DayEmails To Send

This Table shows a scenario if you wanna reach 1K emails per day with a good reputation. Please refer to my Warming up SMTP Guide for more details.

Also, you can watch my full video about Warming up here:

rDNS (Reverse DNS):

The reverse DNS is called a pointer record and is used to point your IP to your Domain, its the inverse of the regular DNS A record.

So when you call the IP, you will get the name. It is also an essential factor in setting up your mail server and increasing your sending score and reputation.

Learn more about rDNS here:

DMARC (Domain-based Message Authentication, Reporting & Conformance):

It is a Protocol that uses (SPF)  and (DKIM) to determine the authenticity of an email message. 

DMARC makes it easier for Internet Service Providers (ISPs) to prevent malicious email practices, such as domain spoofing in order to phish for recipients’ personal information. 

It allows email senders to specify how to handle emails that were not authenticated using SPF or DKIM. Senders can opt to send those emails to the junk folder or have them blocked them all together.

To understand the importance of DMARC for your Online Business and how to set up, please watch this video:

MX Record

Mail Exchange (MX) records are DNS records that are necessary for delivering email to your address.

In simple DNS terms, an MX record is used to tell the world which mail servers accept incoming mail for your domain and where emails sent to your domain should be routed to. If your MX records are not pointed to the correct location, you will not receive an email.

Avoid Spam Factors

Mainly we have Four main factors the determines your spam score:

  • IP Reputation
  • SPF, DKIM, rDNS, and DMARC.
  • Message Body
  • Email List health.

The first two factors are explained above. we still have Message body and Email List Health.

Message body

Simply is the subject and the content of your email. does it look spammy? does it have any spammy keywords and triggers?? this what determines your message score.

Be sure to avoid any of these while creating your Subject lines and Message bodies.

Check this article on Hubspot, to learn more about spam keywords.

You Maybe Also Interested in this article “How To Land Your Emails In Inbox? The Ultimate Guide!”

Email List Health

Simply it's determined by two things:

  • Bounce Rate: How many emails are valid in your list.
  • Spam Traps: does your list contain any spam traps?

Learn more about spam traps and how to avoid in this video:

And always be sure to validate your email lists and clean it before sending any campaign. check my free online email validation service here.

I think you will be also interested in watching this video:

How to send 100K emails Daily to inbox.

Follow up My Youtube Channel For Daily Awesome new videos about Email Marketing, Digital Marketing, and Online business stuff to Grow Online.

Also, Join My Email Marketing Newsletter to Get exclusive Email Marketing Tips that I share only with my email subscribers.

Optional (IF YOU USE NGINX): 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!

Good Luck!