What You Need to Know About Custom Domains and Subdomains

One of the first decisions you’ll encounter when using a new email service provider (ESP) or setting up your email marketing strategy is whether to create a custom domain and subdomain. You’ll find them recommended often, but sometimes with little explanation about how or why you should use them. And the key question - what’s the difference?

Setting up both a custom domain and a subdomain will be a key piece in your overall email deliverability strategy, helping you make sure that your emails are landing in subscribers’ inboxes. Here we’ll help you decipher how to use them to your advantage, so stick with us!

Custom Domains

Domains are unique identifiers for your website (for example, www.thisisadomain.com). If you have an ecommerce business, there’s a good chance you already use a domain for customers to shop with you online. In an email address, the domain is what you’ll find after the @ symbol (for example, in anna@thisisadomain.com).

Internet service providers (ISPs) like Gmail or Outlook are moving away from IPs when determining a senders’ reputation and primarily looking at these domains, since they're more brand-specific. If your domain is associated with negative activity like spamming subscribers or sending emails without an unsubscribe link, then your overall reputation will be poor and your emails are far more likely to end up in the spam folder.

Read more: The 2019 Ultimate Guide to Email Deliverability

When you start using a new ESP, your emails will by default be sent over their shared domain, meaning you have little control over its reputation and, therefore, your deliverability. This is why you should use an ESP that takes care of their shared IP pool, but it’s also where using a custom domain like your website’s will save you!

Using a custom domain instead of the shared domain will allow you to control the sender your subscribers see, as well as that domain’s reputation in the eyes of ISPs. You should be able to include your domain as a custom “from” email address in your ESP’s settings and connect it through your domain name system (DNS).

Related: How to Set Up a Custom Email Domain in Hive

With Hive, emails sent on your custom domain will automatically be sent through a “warmup” process, ensuring that ISPs don’t see a sudden wave of emails being sent and mark them as spam.


You may have heard us speak about subdomains before - they’re an essential piece of any holistic deliverability strategy, and an easy way to shield your primary domain from added risk. You can find subdomains as a prefix in front of a primary domain (for example, the “mail” in anna@mail.thisisadomain.com). Many email marketers don’t use subdomains, but we’re big fans and would encourage you to set one up.

Read more: Why You Should Be Using a Subdomain

ISPs look at your subdomain as a unique entity when establishing your sender reputation, meaning that a misstep for your subdomain won’t irreparably harm your primary domain’s deliverability. If you accidentally send a large email blast to an unengaged audience, for example, ISPs may mark your emails as spam. Using a subdomain here would ensure that other emails being sent through your primary domain, which is likely a key component of your brand, won’t be affected.

This is also helpful to make sure the most important emails still hit subscribers’ inboxes. Transactional emails (like purchase confirmations) statistically have a much higher rate of engagement than marketing emails. Creating a unique subdomain for each email objective will ensure that the engagement levels of one won’t negatively affect the deliverability rate of another.

Another trick to keeping each type of email separate is to break them out into different accounts whenever possible. This’ll prevent you from accidentally sending an email from the wrong subdomain, potentially hurting its deliverability, and will also let you keep your templates and reporting isolated by objective for a more targeted strategy.

Like with your main domain, you’ll want to warm up your subdomain so your emails aren’t marked as spam. We recommend sending to your subscribers in regular, increasing intervals to build a strong sender reputation and avoid being sent to junkmail.

Read more: How to Warm Up a New Subdomain

Wrap Up

Custom domains are a popular, but crucial, piece in many marketers’ email strategies, allowing you to put your brand face-forward and take control of your sender reputation. Subdomains are under-utilized, but act as the perfect complement to protect your primary domain. Together, they establish the foundation for a holistic deliverability strategy, ensuring that your carefully designed emails actually reach your subscribers.

Learn more about boosting your deliverability strategy in our 2019 Ultimate Guide to Email Deliverability! In it, we take a closer look at how to build a strong sender reputation and avoid being blacklisted (complete with checklist).

Hive's Ultimate Guide to Email Deliverability