---
title: "Top Level Domain (TLD)"
description: "Top Level Domain (TLD) is the last part of a DNS address (.com, .net, .org, etc.) indicating purpose or location of a domain."
url: "https://mailmum.io/glossary/top-level-domain-tld/"
---

# Top Level Domain (TLD)

A Top Level Domain (TLD) is the last segment of a domain name, representing the
highest level in the domain name system. It typically consists of two or more
letters and indicates the purpose or geographical location of a website or
entity. Examples include .com, .org, and .net. TLDs help categorize and organize
websites on the internet, facilitating easy navigation and identification.

## What types of TLD are there?

TLDs fall into two groups that are worth keeping apart, because they are run by
different kinds of organisation under different rules:

* **Generic TLDs (gTLDs)** such as `.com` or `.org`. Some are open to anyone,
  others are sponsored and restricted to a defined community.
* **Country code TLDs (ccTLDs)** such as `.de` or `.jp`. These are derived from
  the two-letter country codes in ISO 3166-1 and are administered by a registry
  in or on behalf of that country or territory.

## What are typical popular TLDs and their envisioned use case?

Generic TLDs and their envisioned use cases:

* `.com` - commercial/business websites, in practice used for anything
* `.org` - non-profit organizations, open registration
* `.net` - network infrastructure or service providers, open registration
* `.info` - informational websites, open registration
* `.biz` - business-related websites
* `.gov` - US government entities, restricted
* `.edu` - US-accredited educational institutions, restricted
* `.mil` - US military organizations, restricted
* `.int` - international treaty organizations, restricted

Country code TLDs:

* `.uk` - United Kingdom
* `.ca` - Canada
* `.de` - Germany
* `.jp` - Japan
* `.fr` - France
* `.cn` - China
* `.co` - Colombia. Widely marketed and used internationally as a short
  alternative to `.com`, but it remains Colombia's ccTLD.
* `.io` - British Indian Ocean Territory. Popular with technology and startup
  companies, and treated as a generic TLD by most people who register one. Note
  that its long-term future is tied to whether the territory keeps its ISO
  3166-1 entry following the 2024 agreement between the UK and Mauritius over
  the Chagos Archipelago. If you are choosing a domain for infrastructure that
  should still be there in ten years, that is worth factoring in.

Please note that this list is not exhaustive. There are well over a thousand
TLDs, including many newer generic TLDs introduced since 2013.

## Is there a list of mail relevant TLDs?

Spamhaus publishes reputation statistics that break down abuse by TLD, which is
a good way to see which TLDs are currently dominated by spam and malicious
registrations: [Spamhaus Reputation
Statistics](https://www.spamhaus.org/reputation-statistics/).

This matters because some receiving systems and filtering rules score mail from
badly-behaved TLDs more harshly, regardless of how well your own server is
configured.


## What is a good TLD for a mail server domain?

This is dependent on the use case you have. We recommend using customer domains
for single mail systems of a company. If you want to run a general purpose
system with hundreds or even thousands of clients, then `.net` or `.com` are a
good choice, as they are long-established and carry no inherent penalty in spam
filters.

Two practical points:

* Prefer a TLD with a stable registry and a low abuse rate. A cheap TLD with a
  bad reputation costs you deliverability you then have to win back.
* Keep the mail server [hostname](https://mailmum.io/glossary/reverse-dns-rdns/) on a domain you
  actually control the DNS for, so you can set matching forward and reverse DNS
  records.

That said, the TLD is a minor factor. If a domain is abused for spam, the
system will get into trouble regardless of which TLD it was set up on.

## How do you block a whole TLD in Postfix?

Rejecting mail by TLD is a blunt instrument, but for a server with a known user
base it is effective and easy to reverse. Two separate cases, with a how-to
each:

* [Howto block entire TLDs in Postfix](https://mailmum.io/posts/howto-block-entire-tlds-in-postfix/)
  — rejecting *senders* whose address is in a given TLD, using
  `smtpd_sender_restrictions`.
* [Howto block mailservers using uncommon TLDs in hostname through
  Postfix](https://mailmum.io/posts/howto-block-mailservers-using-uncommon-tlds-in-hostname-through-postfix/)
  — rejecting *servers* that greet with a
  [hostname](https://mailmum.io/glossary/hostname/) in that TLD, using
  `smtpd_helo_restrictions`.

The two are not interchangeable: the first looks at the envelope sender, the
second at the connecting server's identity.