What is mail server?

Updated at: May 15, 2020
By Gatefy

An email server.

We could say that a mail server is your digital post office. It's a machine or an application responsible for handling messages. In other words, a mail server, also called email server, receives and delivers emails, this is its function.

So, when you send an email, your message usually goes through a series of email servers until it reaches the recipient.

The process is so fast and efficient that it looks simple, but there's a lot of complexity behind sending and receiving emails.

To avoid confusion, it's important to be clear that the term mail server can have different meanings depending on the context. At times, an email server can mean a computer or a machine that has a complete system that includes several services or applications.

At other times, the term email server can be used precisely as a synonym for some of these services or applications.

In this post, we'll talk more about the following topics:

  • Types of mail servers.
  • SMTP.
  • POP3.
  • IMAP.
  • How is the process of sending emails.
  • Email security.

Types of mail servers: outgoing and incoming servers

When we use the term email server in the sense of services or applications, we may separate email servers into 2 main categories: outgoing email servers and incoming email servers.


Outgoing email servers are called SMTP servers (Simple Mail Transfer Protocol).

On the other hand, incoming email servers are known by the acronyms POP3 (Post Office Protocol) and IMAP (Internet Message Access Protocol).

Before you ask yourself what's the main difference between IMAP and POP3, we'll tell you. With IMAP, messages are stored on the server itself. While with POP3, messages are usually kept on the device, that is, on your computer or cell phone.

In general, IMAP is more complex and flexible than POP3. 

How is the process of sending emails in 4 steps

To facilitate understanding, we've created a basic step-by-step of the email sending process. It's a very simplified version, but it allows you to understand how an email is sent and delivered. Check it out.

Step 1: Connecting to the SMTP server

When you send an email, your email service or platform, such as G Suite, Exchange, Office 365 and Zimbra, will connect to the SMTP server. That SMTP server is connected to your domain and has a specific address, such as smtp.gatefy.com or smtp.example.com.

At this stage, your email service will provide the SMTP server with some important information, such as your email address, the body of the message and the recipient's email address.

Step 2: Processing the recipient's domain

Now, the SMTP server will identify and process the recipient's email address. If you’re sending an email to someone else in your company, that is, to the same domain, the message will be directed to the IMAP or POP3 server.

Otherwise, if you're sending the message to another company, for example, the SMTP server will need to communicate with that company's email server.

Step 3: Identifying the recipient's IP

At this stage, your SMTP server will need to connect with DNS (Domain Name System) to find the recipient's server.

The DNS works like a translation system. Basically, it'll help to convert the recipient's domain into an IP address. By the way, IP is a unique number that identifies a machine or server connected to the internet.

SMTP needs IP to perform its function correctly, thus being able to direct the message to the recipient's server.

Step 4: Delivering the email

Not everything is as simple as it seems, though. Generally, your email will go through different unrelated SMTP servers until it reaches the recipient's SMTP server.

When it receives the email, the recipient's SMTP server checks the message and then directs it to the IMAP or POP3 server. Then, the email enters a queue, being processed until it’s available for the recipient to access.

Okay, now the email can be read. And you know the basics about incoming and outgoing mail servers. But, to conclude, we still need to talk about email protection.

Email security

We've shown you here a simplified process. Sending and receiving emails involves different and complex processes and protocols, which, unfortunately, are usually forged.

In fact, email is the main vector for cyber attacks, the most used way by criminals and attackers to commit scams and fraud.

It means that, if you have a business and want to keep it free from threats, you need to be careful about email protection. Your business's email security needs to take into consideration several aspects, from creating internal policies for the use of email to adopting protection solutions.

If you use G Suite, Office 365, Exchange or Zimbra, for example, read more about how to strengthen the protection of these platforms and, consequently, your company's information and data.

If you’re interested in this subject, Gatefy can help you. Contact us to find out more.