Mail Transfer Agent: What Is It And How Does It Work

Boost Inbox Logo Mia Anderson
December 28, 2023
White mail over the screen of the laptop.

An MTA is basically a super assistant for emails. You write the email, it takes it and delivers it to the right place, lik a friend helping you send a letter!

In the world of email, there are behind-the-scenes players that ensure that your messages reach their intended destinations. One such key player is the Mail Transfer Agent (MTA).

In this blog, we will discuss what a Mail Transfer Agent is, how it works, why it's important, the difference between MDA, MTA, and MSA, and some mail transfer agent examples.So let's start

What Is a Mail Transfer Agent (MTA)?

A Mail Transfer Agent (MTA) is a software application responsible for routing and transferring email messages from one computer to another within a network or across networks. MTAs follow the Simple Mail Transfer Protocol (SMTP) standards to handle the sending, receiving, and routing of emails.

When you send an email, your email client communicates with an MTA, which then routes the message through the internet to the recipient's MTA. The recipient's MTA then delivers the message to the recipient's email server or mailbox. Popular examples of MTAs include Sendmail, Postfix, Exim, and Microsoft Exchange Server.

Alright, so now that we've covered the techie stuff, let's put it simply.

Think of a Mail Transfer Agent (MTA) as a post office for emails. When you send an email, the MTA is like the postman who takes your letter and makes sure it gets to the right place. It's responsible for sending your email to the correct email address on the internet. So, just like how a post office routes letters to their destinations, an MTA routes emails to the right email servers or mail

Once your email reaches the recipient's MTA, it's delivered to their email inbox just like how the postman delivers your letter to your friend's mailbox. MTAs make sure emails get where they need to go on the internet, making communication through email possible!

How Does a Mail Transfer Agent Work?

After understanding the mail transfer agent Let's dive deeper into the inner workings of an MTA.

When you hit the "Send" button on your email client, the MTA first verifies the recipient's email address. It performs various checks to ensure that the email is going to a valid and active account.

These checks include verifying the domain's existence, checking for typos, and scanning for spam indicators.

Once the recipient's email address is confirmed, the MTA begins the transfer process. Connects to the recipient's email server using the SMTP protocol.

It sends the email over a series of hops, which are intermediate servers responsible for transmitting the message across the Internet. These hops act as checkpoints and ensure that the email is sent to the correct destination.

The MTA encodes the email during transmission in a defined format known as Multipurpose Internet Mail Extensions (MIME).

It enables MTAs to include attachments, format emails, and handle other capabilities such as HTML formatting. This ensures that the email is delivered to the recipient in a legible and accessible format.

If the recipient's email server is temporarily offline or unreachable, the MTA will queue the email for future delivery.

Once the server is back online, it will retry sending the email. If the server remains unreachable for an extended period, the MTA will route the email back to the sender, notifying them of the unsuccessful delivery.

Why Are MTAs Important?

MTAs play an important role in the reliability and efficiency of email communication. Here are a few reasons Why Are MTAs Important.

Reliable Email Delivery:

MTAs ensure emails are delivered to their intended recipients without mistakes or delays by handling the complex process of message routing.

They provide a trustworthy and scalable solution for managing enormous amounts of emails across several mail servers.

Spam and Virus Filtering:

MTAs are equipped with powerful spam and virus screening algorithms. They monitor incoming emails for suspicious content and filter out potentially dangerous or unwanted messages.

This helps to keep spam out of users' inboxes and protects them from dangerous threats.

Error Handling and Diagnostics:

MTAs give strong error handling and diagnostic features. They create bounce-back messages, also known as Non-Delivery Reports (NDRs), to notify senders about failed delivery of emails.

These reports provide useful information such as delivery status, problem codes, and extensive logs that assist users in troubleshooting and resolving delivery difficulties.

Email Routing and Redirection:

MTAs provide several routing and redirection options. To simplify email administration, businesses can utilize forwarding rules, aliasing, and distribution lists.

Emails may be defeated by many recipients or particular departments using these tools, guaranteeing effective internal communication.

What Is the Difference Between MDA, MTA, and MSA?

While MTAs are a crucial component of email delivery, it's important to understand What Is the Difference Between MTA, Mail Delivery Agent (MDA), and Mail Submission Agent (MSA).

Mail Transfer Agent (MTA):

As discussed earlier, the MTA is responsible for routing and transferring emails between different mail servers.

It handles the transmission process, ensuring that emails reach the appropriate destination.

Mail Delivery Agent (MDA):

The MDA receives incoming emails from the MTA and delivers them to the recipient's mailbox. It is responsible for storing and organizing the emails on the recipient's email server.

The MDA allows users to access their emails through protocols such as POP3 or IMAP.

Mail Submission Agent (MSA):

The MSA is responsible for accepting outgoing emails from the sender's email client or application.

It authenticates the sender, performs many necessary checks or configurations, and hands over the email to the MTA for further processing and delivery.

These three components work together seamlessly to ensure the secure and efficient transfer of emails from sender to recipient.

Mail Transfer Agent Examples

Now that we have a better understanding of what MTAs are and how they work, let's explore a few popular mail transfer agent examples.

1. Exim:

Exim is a good mail transfer agent example a popular open-source MTA known for its scalability and versatility. It has extensive routing, filtering, and authentication functions. Exim, which runs many email servers, is well-known for its reliability and efficiency.

2. Postfix:

Postfix is another famous open-source MTA that is utilized by businesses of all sizes. It focuses on security, setup simplicity, and resource efficiency. Postfix has a significant and active user community and substantial documentation.

3. Sendmail:

Sendmail is one of the oldest and most well-established MTAs. It has a rich history and has played a significant role in the development of email systems. It offers a robust feature set and is known for its stability.

4. Microsoft Exchange Server:

Microsoft Exchange Server is a comprehensive email solution used by many businesses. While it includes various components, it incorporates an MTA to handle email routing and delivery across Exchange servers.

These are just a few mail transfer agent examples in the market. Each MTA offers unique features and capabilities, allowing organizations to use their email infrastructure for their specific needs.


In short, Mail Transfer Agents (MTAs) are essential for the reliable and safe transmission of emails. They are in charge of email routing and transmission, as well as ensuring that messages reach their intended recipients.

They are required for effective communication, spam protection, error management, and email routing.

Understanding the differences between MTAs, MDAs, and MSAs aids in comprehending the many phases of email delivery. Organizations can select from several MTAs, including open-source options such as Exim and Postfix, as well as commercial solutions such as Microsoft Exchange Server which are the mail transfer agent examples.

What to read next

Yes, Boost Inbox is designed to cater to businesses of all sizes and industries.

Absolutely! Boost Inbox is compatible with most major email service providers.

The warmup process duration may vary depending on your email volume, but it typically ranges from a few days to a couple of weeks.

Yes, Boost Inbox offers dedicated customer support to assist you throughout the warmup process.

While it's possible, it's best to start the warmup process from the beginning with Boost Inbox for optimal results.