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The key concepts for email domains

Understand the key concepts associated with domains

What is a domain?

A domain is the main web address that identifies a website or organisation on the internet. For example:

  • nytimes.com
  • bbc.co.uk

Domains are used to provide an identifiable address hosted websites and email. 

When Echobox sends emails on behalf of a client, those emails must be authenticated using the client's domain to prove to inbox providers that the emails are legitimate.

What is a subdomain?

A subdomain is a subdivision of a main domain, and always appears before the main domain name.

For example:

  • Main domain: theguardian.com
  • Newsletter subdomain: newsletter.theguardian.com

Should I use a top-level domain or a subdomain?

It is typically recommend to use a dedicated email subdomain rather than the main brand domain. The key reason is reputation isolation.

Why this matters Email providers (Gmail, Outlook, Yahoo) assign a reputation score to each sending domain based on factors like spam complaints, bounce rates, and engagement.

If email reputation decreases, it affects only the email subdomain — not the main brand domain and website.

One important consideration: a new subdomain starts with a neutral reputation, with no sending history. To build a positive reputation from scratch, clients should:

  • Start by sending to small volumes of highly-engaged readers
  • Gradually increase sending volume over several weeks
  • Extend scope to less-engaged readers only after a strong reputation is established

This process is called inbox warming, and it's a normal part of setting up a new sending domain.

What is DKIM?

DKIM (DomainKeys Identified Mail) is a security method that verifies an email genuinely comes from the domain it claims to come from. Think of it as a digital signature on every email.

How it works

When DKIM is set up:

  • Echobox signs each outgoing email with a private cryptographic key
  • The client publishes the matching public key in their DNS records
  • When an inbox provider receives the email, it checks the signature against the public key
  • If the signature matches, the email is verified as authentic

What DKIM confirms The email was authorised by the domain owner. The email content was not altered in transit.

DKIM in Echobox

DKIM is mandatory for all Echobox Email clients. After a Property is created, the required DKIM records appear in:

Settings → Property → Domain Verification

Our guide for how to configure DKIM corrrectly can be found here.