Subdomains and deliverability


Using subdomains for email sends is a great way to boost your deliverability and reputation as an email sender. 

In this article, you'll learn what subdomains are and how to use them to achieve high deliverability rates.

What are domains and subdomains?

A domain (sometimes called a base domain or root domain) is a unique identifier that categorizes an entity, such as a company website. For example, "" is a base domain. Domain reputation helps mailbox providers decide whether to accept your mail, deliver it, mark it as spam, or block it outright.

A subdomain is an extension of the base domain. For example, in the web address, "," the subdomain is “news.” Subdomains are key in building a strong sending reputation across your different email types (which are also sometimes called "mail streams").

Using subdomains can help you minimize potential domain reputation issues and make sure your mail goes where you want it to go.

Why use a subdomain?

One way to help keep your domain reputation high is to segment your email types and use subdomains for sending different campaigns. For example, you can use the subdomain "" to send blog updates to your audience or use "" to alert your audience about upcoming events in their area. This gives you better control over your domain reputation. It is also an industry best practice that we strongly recommend.

Subdomains are used by email marketers who want to assign a unique name or subset to a specific email type. The domain owner can assign a subdomain to a specific email type and manage this as a separate domain from their base domain (with its own reputation).

How do subdomains influence your sender reputation?

Your subdomain reputation(s) can impact base domain reputation, but the impact between subdomains will be small. Subdomains are not a way to avoid a bad domain reputation. Instead, they will help differentiate your traffic while maintaining a clear relationship with your main domain.

Subdomains should be treated as an extension of the base domain. Subdomains should be managed with best sending practices to ensure high deliverability across your different types of emails. You can manage your domain reputation using deliverability monitoring tools such as Google Postmaster Tools to track subdomains separately. It can help you identify pain points, reputation shifts, and other activities that could potentially harm your deliverability.

What are some use cases and strategies for subdomains?

Sending different types of emails through specific subdomains is important because this can help lower the risk of an underperforming marketing email overpowering and negatively impacting other emails that have actions to be completed, such as password resets.

You can use subdomains for different email use cases, like:


  • Examples include order confirmations, password resets, and delivery notifications
  • Typically have the highest engagement rates and lowest spam complaint rates
  • Use the Postmark CX App integration to send transactional emails from automations in ActiveCampaign

Batch sends

  • Examples include newsletters, promotions, new products, and brand updates
  • These see varying engagement rates based on segments, content, and other deliverability factors

Corporate emails

  • Examples include corporate mailings with customers, vendors, and prospects
  • These emails see high engagement rates because they contain high-value information such as internal content, legal documents, and proprietary information 

Since you don't want bulk sending (like a mass audience update) to negatively influence your corporate emails, you should create multiple subdomains (, to use for your other types of emails and leave the base domain ( to the corporate mailing only.

Keep in mind that you need to have substantial and consistent volume in order to make this type of strategy effective. Frequent reputation shifts between the subdomains can influence the base domain reputation in a negative way.

Looking for more reputation resources?

Subdomains are a critical part of building and maintaining a high sender reputation. For more information on overall domain reputation, please read the Email Sending Reputation: How Does Domain Reputation Work? blog post. 

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