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Best Mail Servers for Linux OS

In this article, we will go through the top Linux mail servers that can be implemented on your servers.

14 Dec, 21 by Elizabet J 16 min Read

List of content you will read in this article:

In our mobile-first world, we can send and receive information from one corner of the world to another by simply hitting a "Send" button. Most of us enjoy these features of social media applications and email systems, but we give it no thought to understand the mechanism constructed behind the scenes. If we consider an email message, we need to look at how the message travels from its point of the organization to its destination. 

Before diving into some long-established technical standards, we can be sure of before diving because there would be more than one checkpoint for the message to reach its final destination. In technical terms, these checkpoints are called mail servers. And the point of the organization is known as an email client. You can treat a mail server as a friendly mailman who takes multiple turns before delivering your mail. 

Now, when we consider multiple mail servers, we need to understand how they communicate and what kind of protocols are in place to authenticate each message. This article will share some insightful information on mail servers and help you decide the best-suited mail server for your business. 

Mail servers or email servers is a computerized system that can send and receive emails. This system is usually a combination of many interconnected servers, and they help each other in sending the message to the right recipient. The process of sending an email may take only one second, but it involves a series of transfers from one mail server to another. If you take away the rest of the mail servers that are not within your domain reach, you are limited to send emails to only those people whose email address matches your domain. 

Email clients are quite different from a mail server as they help messages travel over the internet through multiple servers to reach the final recipient. They do not handle any storage facilities like the servers, and they must be connected to the shared network. Some of the most common email clients are Outlook and Gmail. These email clients create an interface for users to organize and categorize their messages. One can even handle attachments like images or documents into their messages using an email client. 

An email server can be set up on a:

We recommend the last two options as it is much more reliable and unlike a home computer, these servers are online 24/7 and are hosted on premium datacenters equipped with enterprise hardware. 

The email mechanism has been around for decades, but it always came with some other limitations. If we dial back a couple of decades, we will witness only a single mainframe system for sending and receiving messages. Now, we follow unique protocols that allow us to form interconnections between different mail servers. By forming a shared network with multiple mail servers, we have integrated the internet to allow the servers to communicate. This communication channel is not a single-step operation, and it flows through a series of servers to reach its destination. To make it easier for you to understand, we have highlighted the message flow step-by-step. 

Step 1- Writing of emails is done using an email client. It can be from Apple Mail or Google's Gmail. After you write your message and hit the send button, your email client automatically connects to your domain's server. 

Step 2- The server then interacts with the client to attain information such as the recipient's email address, the body of the message, and any attachment. This is done to help the server locate the recipient's destination. 

Step 3- To initiate the transfer, the server follows a standard protocol called "Simple Mail Transfer Protocol." SMTP involves the server searching for the recipient's domain name and locating the final server near its destination. The recipient's domain name is acquired using a DNS server, and it makes contact with the destination mail server, which is also known as Mail Exchanger (MX). 

Step 4- After the mail transfer agent locates and delivers to the final destination, the recipient accepts the message through two main protocols: Post Office Protocol (POP) and Internet Message Access Protocol (IMAP). 

The SMTP servers play a huge role in sending and receiving messages because they perform scans at both ends to authenticate the usernames and domain names. The protocols change for each organization, and it is necessary to align your requirements with an emailing process. 

Many people wonder why installing mail servers is beneficial. It is not their fault because we can argue that the cost of hardware and electricity can be a bit too much from one perspective. This may be true for small business managing a couple of hundred mail accounts, but in other cases, mail servers provide immense value, and here are some advantages to prove it:

  • You get your emails instantaneously, and there is no delay at all. When you install a mail server with your domain name, all outside mails will directly come to you, with zero waiting time. If you don't have a mail server in place, the sending machine will likely implement a back-off algorithm that makes the message bounce from one server to another. The time delay will increase in such cases, and a bad internet connection would only cost you more. 
  • Internal mails are sent to the destination instantly after hitting the send button. Everyone is likely to have the same domain name within an organization, so having a mail server can process the message almost instantly. The best part about using mail servers for internal communication is it does not depend on Internet access and attachment size. 
  • Mail servers give you complete control over the list of users so that you can add or delete users at any given point in time. This usually is not possible with Internet Service Providers because they limit how many users you can have at your end. 
  • Mail servers take care of spam filtering and virus scanning to another level that no ISP can match. The problem with an ISP is that they have complete control over authentication and scanning operations, but with a mail server, you will be the one to take over. 
  • Special emails for printers and faxes can also be executed using your mail server. You can automatically print a copy and send a fax of requested documents. 


In the last decade or so, mail servers' functionality drastically increased from sending, receiving, and providing access to different messages. These servers' functionality is always associated with core features such as POP, SMTP, and WebMail. Still, you can also add specific functionalities for your mail server to maximize its potential. 


When you are an organization looking to expand, you have to consider the scalability factor to support thousands of users. To understand the scaling of mail servers, you need to know your company's product support system and monitor the IO subsystem's performance. These can help give you a fair idea of how much more hardware you require to meet your requirement. To have a more precise number, you should also consider the logging and service usage level. 

Ability to Integrate

If you spend a fortune on mail servers, you likely want to integrate it with other software to ease business operations. To know whether a mail server can co-exist with other software, you need to assess the mail server's architecture and inner workings. Speed and efficiency can be used to determine whether a mail server has the required architecture to integrate third-party software successfully. 

Migration Facilities

If you are requested to transfer data from one mail system to another at some point in time, it will cost you a lot of money. That is why you should choose a server having migration facilities with either MBOX or MDIR format. You can also migrate configuration data if the servers have access interfaces. 


Security features are highly important when it comes to managing mail servers. Many providers give not one but several authentication features to restrict unauthorized access. You should also consider having a responsive alert system for your mail server. This way, you are immediately notified when there is a security issue. Few other security features to consider are IP-based authentication, SMTP filtering, and RealTime Black-Lists. 

We highly recommend having a read at the difference between Bulkmail and Spam in order to further understand the mechanisms of mail servers and 'mail' itself. 

AntiVirus and AntiSpam Management 

Preventing malware from entering your mail server is important because it can leak confidential messages to other servers. Some features to consider for antivirus management are attachment control, auto download of virus definition files, and multi-scan options. In the case of anti-spam management, you should look for download filters, sender checking, and mail reports. These tools can help you in any situation or emergency. 

Now that you are clear with all the basic concepts surrounding mail servers, we are ready to dive into some of the best mail servers the marketplace has to offer. 

To get a reliable mail server for your business and organization, you need to consider several features and do some heavy research around them. To save you some time, we have created a list of the best mail servers that meet basic functionality and more. 

1.   Exim 

One of the top-rated mail servers in the marketplace by many experts is Exim. It is a mail server with various features to offer, and each of them perfectly executes a specific operation. The most significant advantage of using Exim as your mail server is customization and configuration abilities. 

They have the best transfer agents capable of adapting to any business environment, making it easier to customize. As this is a Linux-based mail server, the GNU GPL license creates administrators' opportunities to modify the original software. 

2.   Sendmail

Sendmail is another top pick in our best mail servers list because it is the most reliable mail server. As it doesn't need high network bandwidth, Sendmail can batch different addresses to a single host machine. 

When it comes to customization, it uses the configuration files to run the instructions. Sendmail is also popular for its delivery methods, which follow standard protocols. 

3.   hMailServer

Free mail servers are also reliable for global operations, and one of the most flexible mail servers is the hMail server. It being open-source allows everyone to download the software without spending a penny. 

The main protocols in use for hMail servers are IMAP, SMTP, and POP3. The ability to integrate is present, and on top of that, it can also run multiple antivirus scans on incoming and outgoing emails. 

4.   Mail Enable

Mail Enable is another free mail server for Windows operating system. With this option, you have no limits for domains and users, and it also brings in the powerful administrative software. Mail Enable is easy to install, and the standard edition of the software can be used for personal and business purposes. However, it is recommended to opt for enterprise premium to avail more features that offer higher flexibility. 

Mail Enable is an excellent mail server with an advanced AJAX webmail client, but we suggest you add a decent spam filtering feature and an email archiver appliance or VM. 

5.   Axigen 

A robust mail server that comes with many innovative features is Axigen. It takes email management to another level by having a massive collection of predefined functions for specific operations. Axigen also comes with various mobile capabilities, which would make it more compatible with other platforms and systems. 

The free edition of Axigen is limited to only five users, so you better go with a professional plan to access all features. The interface of Axigen is easy to understand and navigate. There is a tool for everything, and it considers modern-day features like multi-layer access control as well. 

6.   Zimbra 

Zimbra is another open-source software on our list, but this is more powerful and efficient than a Linux distribution. Zimbra creates a friendly environment for its users by providing additional features like group calendars and convenient UI menus. 

The recovery solutions of this mail server are impressive as it focuses beyond security. Zimbra also equips its users with a one-click disaster recovery feature that makes it more reliable in emergencies or server failure. 

7.   Modoboa 

A modern-day mail server that can do everything at a high-efficiency rate is Modoboa. The methods are simple to execute and easy to integrate. To manage its communication channels between components, Modoboa uses a SQL database written using Python. 

Administrators can easily adapt to the new control panel as it comes with a built-in monitor to help users understand the incoming traffic. Modoboa is capable of creating visuals with the help of several filtering facilities. The protocols in place for proper delivery are DKIM and DMARC. 

8.   Apache James 

Apache James is a well-known software foundation with a modern server architecture. It offers a feature-rich mail server that can create unique solutions by adjusting the components. 

Linear scalability is possible with this mail server, and it allows the changes to happen without disrupting the middleware. The configuration allowed to the user is vast, so one integrates well with other technologies having similar calibre. 

9.   Courier Mail Server 

Courier is one of the very few mail servers that provide individual protocols like ESMTP or IMAP for meeting specific requirements and services. Some of the major platforms compatible with courier mail servers are Linux, Mac OS X, and Solaris. 

Admin panel is so much more comfortable to use when compared to other options in this list because it has a wide variety of web-based administration and configuration tools. Courier servers also have a unique filtering mechanism that comes integrated to reduce spam emails. 

10.  Cyrus IMAP Server 

It is another Linux mail server used in organizations having multiple protocol requirements. Cyrus mail servers come with robust system software having powerful mail filtering mechanisms. The software also uses filtering language Sieve to eliminate unnecessary messages present in the users' accounts. 

Two protocols generate the email solutions, and they are CalDAV and CardDAV. An important point to note here is that this software is still in development, so there will be regular updates to fix errors and bugs. 

Mail servers make tremendous contributions towards mail management, and they make it more flexible and easy to operate. The protocols used to carry out the sending and receiving messages are also crucial to land a suitable mail server for your organization. The first step to achieving significant success with your mail server would be to incorporate all the right features. 

If you are having trouble with viruses and spam emails, you need to consider better authentication features with high-level filtering capabilities. We have listed some basic features in this article, but you need to list all the areas you need improvements in and fulfil them with respective functionalities. 

Our top ten mail servers have an excellent chance to increase speed, performance, and security levels. Make sure to check their official websites and explore plans one by one. As a next step, you can check our article on how to run a Linux mail server

Elizabet J

One OF my major goals is getting new experiences about ICT and what’s more making progress through this field.