Best Mail Servers for Linux

Before an email can reach its destination (e.g. your Gmail inbox), it must pass through a number of checkpoints first. These are referred to as mail servers, and the program that enables you to send or receive emails is known as an email client. We can think of a mail server as being a postal worker, the type you see delivering mail day in, day out. They may have to travel some distance and achieve multiple goals before they bring you mail each morning. To explore multiple mail servers, it’s vital that we recognize the way in which they communicate and the protocols set up to ensure each message is authenticated. Below, we’ll explore some essential details on mail servers for Linux to help you find the right one for your company.

What Are Mail Servers?

Mail servers are computerized systems designed to send and receive messages. Systems typically comprise a number of interconnected servers, all helping each other to send an email to the proper recipient.

It’s easy to take this for granted when dashing messages off throughout the day. Yes, actually hitting the send button may only take a second, but the email must undergo several transfers from one mail server to the next (and so on).

Without the mail servers outside your domain reach, you could only send messages to users with email addresses that match your domain.

What Are Email Clients?

Email clients are fairly different from mail servers: they help emails to pass from one server to another until they reach the intended recipient. Unlike the servers, email clients don’t handle storage facilities, and they need to have a connection to the shared network.

Microsoft Outlook and Mozilla Thunderbird are two of the most popular email clients. They (and others) offer an interface through which you can keep your messages organized and easy to find with categorization. You can add or view attachments using email clients too.

The Fundamentals

Emails have been available for decades, though it hasn’t always been as convenient and reliable as it is today. Going back 20 years or so, messages were sent via a single mainframe system, but now we have unique protocols empowering us to create interconnections between a huge number of mail servers.

Building a shared network consisting of many mail servers, we have harnessed the internet to enable communication between servers. This channel isn’t a one-step operation: instead, it passes through a sequence of servers to arrive in the designated inbox. It can be a complex process.

That’s why we’ve created a streamlined message flow, tracking an email’s journey from composition to delivery:

Step 1:

The email is written with an email client, sent from Gmail or Apple Mail. Once you finish composing your message and press the send button, the email client connects to your domain’s server automatically.

Step 2:

This server interacts with the client to gather key details (e.g. the email address for the recipient, the message’s body, and attachments that may be included. This assists the server in locating the destination.

Step 3:

The server follows a standard protocol known as Simple Mail Transfer Protocol (SMTP) to start the transfer. This involves the server running a search for the recipient’s domain name and finding the final server near to the target destination. A DNS server is used to get the recipient’s domain name, and it connects with the destination mail server (known as the Mail Exchanger, or MX).

Step 4:

Next, the mail transfer agent (MTA) finds and delivers the message to its final destination. The recipient accepts it via two main protocols:

  • Post Office Protocol (POP)
  • Internet Message Access Protocol (IMAP)

Both SMTP servers play a crucial part in the delivery and reception of emails, as they perform scans at both ends for authenticating usernames and domain names. The protocols differ for every organization, and you’ll have to align your needs with an emailing process.

What Are the Benefits of  Mail Servers?

You may ask why it’s so beneficial to install mail servers. And that’s fair enough when we consider that the expense of the necessary hardware and energy required can be on the steep side. That’s definitely the case for smaller businesses managing hundreds of mail accounts.

But mail servers deliver remarkable value for money in the long run. Let’s look at some of the major benefits:

  • You’ll receive emails instantly with no delay. All external emails will come to you directly after you install a mail server with your domain name — with NO waiting time. Without a mail server, the sending machine will probably utilize a back-off algorithm that causes messages to jump from server to server. This leads to a longer delay, and this will be worse if you have a weak internet connection.
  • Internal emails are delivered to the destination immediately after the sender taps the send button. Everyone will probably have the same domain name inside a business, so utilizing a mail server can lead to much faster message processing. Plus, leveraging mail servers for internal communications doesn’t depend on the size of attachments and internet access.
  • Mail servers provide you with full control over the users, allowing you to add or delete names whenever you like. With Internet Service Providers, this isn’t the case: they limit the number of users you can set up at your end.
  • Mail servers can implement virus scanning and spam filtering on a level that ISPs simply can’t compete with. The issue with an ISP is that they have total control over scanning and authentication processes — but you’ll take charge when you install a mail server.
  • You can execute special emails for faxes and printers with a mail server. You may print copies or send faxes of documents automatically, for additional communication options.

Questions to Ask Before Choosing Your Mail Server

What is its functionality like?

Within the past 10 years or so, we’ve seen a sharp increase in mail server functionality. They’ve evolved from sending, receiving, and offering access to messages. Mail servers’ functionality is associated with such essential protocols as SMTP, POP, IMAP. You can also incorporate certain functionalities to help your mail server unleash its full potential.

Is it scalable enough?

You need to think about scalability when growing your business, to ensure you can support the communication requirements of many more users. A core component of scaling mail servers is understanding your organization’s product support system and monitoring the performance of the IO subsystem. These can provide you with a good idea of the hardware you’ll need to meet requirements. If you want a more accurate number, you’ll have to explore the logging and service usage level.

Can it be integrated with other software?

Let’s say you pay a lot of money for your mail servers. You’ll probably want to integrate them with other software to make your operations more efficient. You need to analyze the architecture of the mail server and its function to understand if a mail server can work with specific software. You can use efficiency and speed to determine whether or not a mail server’s architecture will allow it to integrate with other software properly.

What migration facilities does it offer?

If you need to transfer data from one mail system to another, that comes with a cost. That’s why it’s best to pick a server with migration facilities, with a MDIR or MBOX format. You can migrate configuration data, too, if the servers feature access interfaces.

What security is available?


One of the most important factors when managing your mail servers is security. A lot of providers include multiple authentication features to prevent unauthorized users gaining access. You should think about implementing a responsive alert system for your mail server, so you’ll receive an immediate notification if a security problem emerges. Other security features that may prove beneficial are SMTP filtering, RealTime Blacklists, and IP-based authentication.

What antivirus and antispam protection is available?

You must stop malware from infecting your mail server to prevent it leaking private emails to other servers. Consider trying attachment control, multi-scan options, and auto downloading of virus definition files for effective antivirus management. With regards to antispam, try sender checking, mail reports, and download filters, all of which can help defend your business.

What Are the Best Linux Mail Servers?

We’ve covered the mail server basis — now let’s explore the best mail servers for Linux. You may find trying to choose a mail server for your company daunting, but it becomes easier with research. You should think carefully about each server’s features and benefits in depth before committing to any one option.

To help make it simpler for you, and save you valuable time, we’ve picked five of the best Linux mail servers on the market.

Courier Mail Server

This is one of the few servers providing individual protocols, such as IMAP or ESMTP, for meeting certain requirements. Courier mail servers are compatible with major platforms like Solaris, Linux, and Mac OS X.

The admin panel is extremely user-friendly compared to some of the other options, as it incorporates different web-based configuration and administration tools. The unique  integrated filtering mechanism combats spam emails too.


Exim is widely considered one of the top mail servers. It boasts a number of features, each capable of executing operations perfectly. The biggest benefit of Exim is the range of configuration and customization options it offers.

Exim is simple to customize as it has the best transfer agents designed to adapt to all business environments. And as it’s a Linux-based server, the GNU GPL license gives administrators the chance to tweak the original software.


Free mail servers are a popular option for obvious reasons. One of the most flexible is hMail server: it’s open-source so anyone can download it without incurring any costs. That’s a massive advantage for any small business working on a tight budget.

The most important protocols used by hMail servers are SMTP, POP3, and IMAP. It’s capable of being integrated efficiently and can run numerous antivirus scans to check emails (both incoming and outgoing).


This is the most dependable mail server available, and deserves its spot in our list of the top five mail servers for Linux.

Sendmail is capable of batching various addresses to one host machine, as it doesn’t demand high network bandwidth. For customization, Sendmail runs the instructions by using the configuration files. Another reason why Sendmail is so popular is its delivery methods, following standard protocols.

Cyrus IMAP Server

Cryus is another of the best Linux mail servers for businesses with a range of protocol needs. These mail servers feature strong software with impressive filtering capabilities, and the Sieve filtering language prevents unnecessary messages reaching user accounts.

The email solutions are generated by a pair of protocols: CalDAV and CardDAV. It’s vital to recognize that this software is still undergoing development, so updates and fixes should address any issues.

Mail servers and Plesk

Plesk is a popular hosting platform that works alongside mail servers, allowing you to run mail servers on the same machine that you use for hosting websites.

The Postfix mail server and Courier IMAP come installed on Plesk for Linux by default. Dovecot and Qmail are also available on Plesk under Linux.

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