---
title: "Mail Transfer Agent (MTA)"
description: "A Mail Transfer Agent (MTA) is a software application responsible for the transfer of email messages between computer systems."
url: "https://mailmum.io/glossary/mail-transfer-agent-mta/"
---

# Mail Transfer Agent (MTA)

A Mail Transfer Agent (MTA) is a software application responsible for the
transfer of email messages between computer systems, using SMTP. The MTA is a
critical component in the email delivery process, ensuring that messages are
routed correctly from the sender to the recipient.

## What is the role of an MTA?

The primary role of an MTA is to accept incoming email messages from a client
application or another MTA and deliver them to the appropriate recipient. This
process involves routing the message through the internet or a local network,
resolving any addressing issues, and ensuring that the message is delivered
successfully.

## Who is running an MTA?

MTAs are typically run by [internet service providers
(ISPs)](https://mailmum.io/glossary/internet-service-provider-isp/), [email service providers
(ESPs)](https://mailmum.io/glossary/email-service-provider-esp/) and web hosting companies, as
well as by individual organizations or even single persons that operate their
own email servers.

Whoever runs the MTA is responsible for how it presents itself to the outside
world: the hostname it uses in the SMTP HELO/EHLO greeting, its [reverse DNS
(rDNS)](https://mailmum.io/glossary/reverse-dns-rdns/) and the reputation of the IP address it
sends from. Those are the same properties that decide whether the MTA ends up
on an [IP blacklist](https://mailmum.io/glossary/ip-blacklisting/).

## What is the difference between an MTA and an MDA?

An MTA is responsible for routing email messages between systems, while an MDA
(Mail Delivery Agent) is responsible for delivering messages to the recipient's
mailbox. The MDA is typically a component of the recipient's email server and
stores the message in the user's mailbox for retrieval.

## What are some popular MTAs?

There are several popular MTAs available, each with its own features and
capabilities. Some of the most widely used MTAs include:

- **Postfix**: An open-source MTA that is known for its security, performance
  and reliability.
- **Sendmail**: One of the oldest and widely used MTAs, known for its
  flexibility and configurability.
- **Exim**: A popular MTA that is known for its ease of configuration and
  scalability.
- **Qmail**: A secure and efficient MTA that is designed for high-performance
  email delivery.
- **Microsoft Exchange**: A commercial MTA that is widely used in enterprise
  environments.

There are many other MTAs available, each with its own strengths and weaknesses
depending on the specific requirements of the organization. Choosing an MTA
depends on the specific needs an organization or individual has.

## Related reading

* [Sending test emails from shell](https://mailmum.io/posts/sending-test-emails-from-shell/)
  — using `mail`, `mutt` and `sendmail` to push a message through the
  local MTA.
* [Manage Postfix mail server queues like a
  pro](https://mailmum.io/posts/manage-postfix-mail-server-queues/) — inspecting, flushing
  and clearing what the MTA has accepted but not yet delivered. See also
  [email queue](https://mailmum.io/glossary/email-queue/).
* [Simple Mail Transfer Protocol (SMTP)](https://mailmum.io/glossary/simple-mail-transfer-protocol-smtp/)
  — the conversation two MTAs actually have.