Customizing a Subdomain

Choose the right subdomains for sending emails to your shoppers.

Updated over a week ago

Within any URL, there’s a domain and a subdomain.

  • A regular domain is a standard URL.

    • Example:

  • A subdomain is a unique portion of a URL that lives in front of the regular domain as a prefix separated by a dot.

    • Example:

You get to choose the subdomains to use when sending emails to your shoppers. Each subdomain gets a distinct sending reputation from the ISP (Internet Service Provider). For example, be sure to create different subdomains for marketing vs. transactional messages, because the mailstreams are different in nature. This ensures that any issue on the marketing subdomain doesn’t impact transactional sends and vice versa.

When choosing a subdomain to send emails from, there are some best practices to keep in mind.


  • Keep your subdomain prefixes minimal.

  • The subdomain you use should be fresh & should not have a prior history of email sent at any other ESP.

    • Why? Because using the same subdomain in different ESPs will cause deliverability issues. Any issue on other ESPs will directly impact the reputation and performance of emails going out through Bluecore.

  • The email subdomain should be a child of your primary domain to make it easier to identify the sender. For example,

  • Don’t use lookalike domains, or domains with such subtle differences it’s hard to recognize they’re separate. For example, has a different parent domain (bluecoremail instead of bluecore).

    • Why? Because lookalike domains are more prone to spoofing or phishing attempts.

NOTE:​​ Only use authenticated domains for sending emails via Bluecore/SendGrid. This is to ensure that the accurate/authenticated subdomain is included in the email header’s From Email. Email messages should PASS all the mandatory DNS Checks like SPF/DKIM/DMARC so there is proper authentication in place.

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