Lesson 4 of 7 2 min read

Choosing Subdomains

Key concepts and best practices for email development.

Keep your transactional sending distinct from the rest of your email by setting up a unique subdomain. This ensures that, if you experience spam issues with your weekly newsletter or drip marketing email infrastructure, critical administrative messages like password resets won’t be interrupted.

We recommend the following structure. We’re using example.com in the table below, but you will use a domain that you will have purchased using a domain hosting service:

Recommended Structure

Messaging goal	Domain category	Sending Domain
• Compliance & security	Transactional only	support.example.com
• Notifications & updates
• Marketing & branding	All other automated and/or bulk mail	mail.example.com

You may absolutely create more subdomains if you like, but for most senders, using two subdomains is ideal. The reasoning behind this:

Engagement benefits: High email engagement leads to better reputation and less spam filtering. Batch-and-blast emails tend to get low engagement compared to automations
Spreading out reputation: This means that sending non-transactional notification emails using the same subdomain as your batch-and-blast newsletter program can help keep your newsletter’s reputation healthy

That said, if you are particularly concerned about siloing your notification mail from your newsletter reputation, you might consider the following structure instead:

Alternative Structure

Messaging goal	Domain category	Sending Domain
• Compliance & security	Transactional only	support.example.com
• Notifications & updates	Product-based automations	updates.example.com
• Marketing & branding	Marketing-based automations & bulk mail	mail.example.com

Once you’ve decided how many subdomains you’d like to set up, it’s time to authenticate them.

How does domain reputation work?

Let’s say you are sending email from hello@mail.example.com. Everything to the right of the @ is considered your “sending domain.” This sending domain can be divided into two parts:

Host domain: This is your main domain - the one you acquire when you purchase from a tool like GoDaddy or Namecheap. In the above example, the host domain is example.com
Subdomain: This refers to the additional, custom information that sits to the right of the @ and to the left of your host domain. In the example hello@mail.example.com, mail is the subdomain
Envelope domain: A second, hidden subdomain ESPs create for technical routing. So while your end users will see emails as delivering from and address like hello@mail.example.com, it will appear to inboxes as something like hello@send.mail.example.com behind the scenes. You generally don’t need to think about this - it only becomes relevant during DNS setup

Each individual subdomain carries a reputation used by inboxes for spam scoring. Using multiple subdomains ensures reputation problems don’t bleed across email use cases or damage your host domain