---
title: "What is an email subdomain and when should you use one"
description: "Learn what an email subdomain is and why it's crucial for transactional emails. Including when to use subdomains and how to set them up."
url: "https://lettermint.co/knowledge-base/deliverability/what-is-an-email-subdomain-and-when-should-you-use-one"
published: "2025-10-20"
last_updated: "2025-10-21"
---

# What is an email subdomain and when should you use one

> Learn what an email subdomain is and why it's crucial for transactional emails. Including when to use subdomains and how to set them up.

When you send emails from your domain name, you probably use an email
address like noreply@example.com. The problem starts when you send both
newsletters and [transactional emails](https://lettermint.co/features/transactional-emails)
from the same domain. A newsletter marked as spam damages the reputation of
your entire domain. This can cause your password resets and order
confirmations to no longer arrive or be seen as spam.

An email subdomain helps you separate different types of emails and protect
your main domain from delivery problems. In this article, we explain what an
email subdomain is, why developers use them, and when you should set up an
email subdomain for your application or website.

## What is an email subdomain

Before we dive into subdomains, let's first explain what a domain is. A
domain is the unique address of your website, like lettermint.co. You use
this domain for your website, but also for sending emails.

**A subdomain is a prefix that comes before your main domain**. For websites,
you might recognize this from addresses like blog.example.com or docs.
lettermint.co. These subdomains point to different parts of your website
while remaining connected to your brand.

The same principle applies to email. An email subdomain looks like this:

```dns-zone
noreply@mail.lettermint.co
```

In this example, `mail` is the subdomain. The email still comes from your
domain, but email providers like Gmail and Outlook treat it separately from
your main domain.

### Root domain vs subdomain for email

The most important difference between your root domain (main domain) and a
subdomain is that they have separate email reputations. Understanding root
domain vs subdomain helps you determine the best strategy for your situation.
Emails sent from `noreply@example.com` (root domain) and
`noreply@mail.example.com` (subdomain) are treated differently by providers
like Gmail and Outlook.

This means that problems with emails from your subdomain don't affect emails
from your root domain, and vice versa. The distinction between root domain vs
subdomain is crucial for developers to keep different types of emails separated
and protect your main domain.

### Email subdomains and sender reputation

Email providers track the reputation of every sending domain. This reputation
determines whether your emails land in the inbox or spam folder. The most
important thing to understand is that subdomains have their own reputation
score, separate from your main domain.

This means that emails sent from `newsletter@mail.example.com` and
`noreply@example.com` build different reputations. If your newsletter is
marked as spam, it has no impact on emails sent from your main domain.

## Why use an email subdomain

As we just wrote, subdomains have their own reputation, separate from your
main domain. But why is that important? Email subdomains give you better
control over your sender reputation and email delivery. These are the main
reasons why developers use them:

### 1. Separate transactional emails from broadcast emails

[Transactional emails](https://lettermint.co/features/transactional-emails)
like password resets and order confirmations are expected within seconds by
users. These emails must always arrive, and preferably faster than light.
[Broadcast emails](https://lettermint.co/features/broadcast-emails)
like newsletters typically have lower engagement. If these emails are marked
as spam, it can damage your sender reputation.

By sending transactional emails from `mail.example.com` and newsletters
from `newsletter.example.com`, you keep these reputations separate. Your
important transactional emails remain reliable, even if a marketing campaign
performs poorly.

### 2. Protect your main domain

You probably also use your main domain (example.com) for personal emails
from your team and colleagues, like john@example.com or
info@example.com. If a marketing campaign damages your main domain's reputation, these personal
emails can also end up in spam. Especially during busy periods like
[Black Friday and holidays](https://lettermint.co/knowledge-base/deliverability/prevent-emails-spam-holidays-gmail-outlook),
spam filters become stricter.

By using a subdomain for bulk sending, you protect your main domain. If
something goes wrong with a campaign, only that specific subdomain is affected.

### 3. Easier troubleshooting

When you send all emails from one domain, it becomes difficult to determine
what causes delivery problems. Are your marketing emails triggering provider
spam filters, or is there a problem with your transactional emails?

### 4. Better organization for larger teams

If you offer multiple products or services, subdomains help keep everything
organized. You might use `app.example.com` for application notifications,
`marketing.example.com` for campaigns, and `alerts.example.com` for
system messages. Each subdomain can be managed independently with its own
sending patterns and volumes.

## When should you use an email subdomain

Not every situation requires a subdomain. Here's when it makes sense to set
one up:

- **You send both transactional and broadcast emails**.<br />


If you send password resets and order confirmations alongside newsletters
or promotions.
- **You send large email volumes**.<br />


With thousands or millions of emails, the risk of reputation damage
increases. A subdomain gives you a safety net. If one subdomain has
problems, your other email types continue working normally.
- **You're launching a new product or service**.<br />


Starting a new project under your existing domain? Use a subdomain from the
start.
- **You have a staging or beta environment** - Testing new features in a
staging environment? Use a subdomain like `staging.example.com` or
`beta.example.com`. This way test emails never affect your production
reputation.

## Tips for email subdomains

If you decide to use subdomains, follow these guidelines:

### Choose clear, professional names

Use descriptive subdomain names that make sense. Good examples are:

- `mail.example.com`
- `transactional.example.com`
- `newsletter.example.com`
- `notifications.example.com`

Avoid confusing names like `xyz.example.com` or using completely different
domains that don't match your brand. Recipients must immediately recognize
that the email comes from your company.

### Set up authentication correctly

Each subdomain needs its own [SPF](https://lettermint.co/knowledge-base/definitions/what-is-spf),
[DKIM](https://lettermint.co/knowledge-base/definitions/what-is-dkim) and [DMARC](https://lettermint.co/knowledge-base/definitions/what-is-dmarc) records.
These protocols tell email providers that your subdomain is legitimate and
help build trust.

At Lettermint, we automatically handle SPF and DKIM setup when you add a
subdomain. You just need to add the DNS records we provide, we handle the rest.

### Warm up new subdomains gradually

When you create a new subdomain, start by sending low volumes and increase
gradually. This builds reputation slowly and prevents your emails from being
marked as suspicious. Also read our article about [greylisting](https://lettermint.co/knowledge-base/deliverability/what-is-greylisting-why-email-delayed)
to understand how email providers treat new senders.

Always test your new subdomain first with our [test email addresses](https://lettermint.co/knowledge-base/deliverability/test-emails-with-our-test-email-addresses-and-prevent-problems)
before sending to real users. This way you can see if everything works
correctly without affecting your monthly usage.

Monitor the [email statuses](https://lettermint.co/knowledge-base/deliverability/understanding-email-statuses-hard-bounce-delivered-pending)
of your new subdomain carefully. Pay special attention to bounces and delayed
statuses in the first weeks.

### Use consistent sender addresses

Don't constantly switch between different email addresses on the same
subdomain. Choose addresses like `hello@mail.example.com` or
`noreply@transactional.example.com` and stick with them. Consistency helps
build recognition with both email providers and recipients.

## Setting up an email subdomain with Lettermint

Adding a subdomain to Lettermint is simple. Here's how it works:

1. **Choose your subdomain**.<br />


Choose something descriptive like `mail.example.com`
2. **Add the subdomain to your Lettermint dashboard**.<br />


Go to [Domains](https://dash.lettermint.co/domains) and add your new subdomain
3. **Add DNS records to your domain**.<br />


We provide the exact DNS records you need to add to your subdomain.
4. **Start sending**.<br />


Your subdomain is ready to use for sending emails!

For more information about setting up DNS records, check our documentation
about [adding a domain](https://docs.lettermint.co/platform/domains/introduction).

## Conclusion

Email subdomains give you better control over your sender reputation and help
keep your most important emails reliable. By separating transactional emails
from broadcast emails, you prevent newsletter problems from affecting your
important transactional emails.

Setting up a subdomain is simple and prevents problems in the future.
Especially if you send both marketing emails and transactional emails, it's
worth keeping them separate.
