Subdomains for Sending: What You Need to Know

A subdomain is a prefix added to your main domain, like mail.yourbusiness.com instead of yourbusiness.com. Some email marketers choose to send from a subdomain to separate their marketing email reputation from their corporate email. This article explains when using a subdomain makes sense and how it affects your email authentication.

Read this article if you're deciding whether to send from your root domain or a subdomain, you want to understand how subdomains affect deliverability, you're setting up a new sending domain and want to make the right choice, or your IT team is asking about subdomain strategy.

A subdomain is a prefix that comes before your main domain name. For example:

Each subdomain can have its own DNS records, including its own DKIM and DMARC settings. From an inbox provider's perspective, subdomains can build their own reputation separate from the root domain.

There's no universally "right" answer. Both approaches have advantages.

Sending from your root domain (yourbusiness.com)

Advantages:

Disadvantages:

Sending from a subdomain (mail.yourbusiness.com)

Advantages:

Disadvantages:

Consider using a subdomain if:

You send high volumes

If you're sending hundreds of thousands or millions of emails, isolating that traffic on a subdomain protects your corporate email if anything goes wrong.

You have multiple email streams

If you send marketing emails, transactional emails, and internal corporate email, you might use different subdomains for each. For example:

You're recovering from deliverability issues

If your root domain has a damaged reputation, starting fresh on a subdomain can be faster than trying to repair the root domain.

Your IT team requires it

Some organizations have policies that marketing must use a subdomain to protect the corporate domain.

Stick with your root domain if:

You're a small sender

If you send a few thousand emails per month and follow good practices, the simplicity of using your root domain usually outweighs the benefits of a subdomain.

You already have good reputation

If your root domain has established positive reputation and you're seeing good deliverability, there's no need to complicate things.

You want maximum brand recognition

Emails from yourbusiness.com may feel more trustworthy to recipients than mail.yourbusiness.com.

Each subdomain needs its own authentication records:

DKIM

You'll need a separate DKIM record for each subdomain you send from. When you add a subdomain in SendX, we provide the specific DKIM record for that subdomain.

DMARC

DMARC can be inherited from the parent domain. If you have a DMARC record on yourbusiness.com, it automatically applies to mail.yourbusiness.com unless you publish a separate DMARC record specifically for the subdomain.

You can also set subdomain-specific DMARC policies using the sp= tag in your root domain's DMARC record. For example:

v=DMARC1; p=reject; sp=quarantine; rua=mailto:dmarc@yourbusiness.com

This sets p=reject for the root domain but sp=quarantine for all subdomains.

SPF

When you send through SendX, SPF is handled automatically regardless of whether you use a root domain or subdomain.

A new subdomain starts with neutral reputation. Inbox providers don't automatically trust it just because your root domain has good reputation. You'll need to warm it up.

Warming a new subdomain

Start with low volumes and gradually increase over 2-4 weeks. Send to your most engaged subscribers first. Monitor deliverability closely during this period.

Reputation isolation

The good news about reputation isolation works both ways. If your subdomain develops problems, your root domain is protected. But it also means your subdomain doesn't automatically inherit your root domain's good reputation.

Some inbox providers do consider parent domain reputation as a factor, but it's not guaranteed. Treat a new subdomain as starting from scratch.

SendX doesn't require you to use a subdomain. You can authenticate and send from either your root domain or any subdomain you choose.

To add a subdomain:

You can authenticate multiple domains and subdomains in SendX. There's no limit.

Does SendX recommend using a subdomain?

SendX doesn't enforce a specific approach. Both root domains and subdomains work well. Choose based on your sending volume, organizational requirements, and how much you want to isolate your marketing email reputation.

Can I switch from my root domain to a subdomain later?

Yes, but the subdomain will need to build its own reputation. Plan for a warmup period when you make the switch.

If I use a subdomain, do I still need DMARC on my root domain?

Yes. Inbox providers look for DMARC on your root domain first. If your root domain has no DMARC record, emails from your subdomain may not pass DMARC alignment. You can set different policies for your root domain and subdomains using the sp= tag.

Will recipients notice if I use a subdomain?

Yes, they'll see the subdomain in your "From" address (e.g., "news@mail.yourbusiness.com"). Most recipients don't pay close attention to this, but it is visible.

Can I use multiple subdomains for different purposes?

Yes. Some organizations use one subdomain for marketing newsletters, another for transactional emails, and another for automated sequences. Each needs its own authentication setup in SendX.

My emails are going to spam. Should I switch to a subdomain?

Not necessarily. First, diagnose why your emails are going to spam. It could be content issues, list quality, or authentication problems. Switching to a subdomain without fixing the underlying issue will just damage the subdomain's reputation too.