How to Warm Up a New Subdomain

If you’ve made your way to this post, you probably know that using subdomains is the best way to separate out your sending reputation for different types of emails (think: marketing or transactional).

Related: Why You Should Be Using A Subdomain

We’re here to break down what you need to be thinking about when setting up a new subdomain. This post takes you step by step through what to consider, how to ramp up sending, and some bonus hacks for building a stellar sending reputation.

Choosing your subdomain

Just to recap: a subdomain is a little different than your main domain.


In the above example, ‘’ is referred to as the “parent” domain. The subdomain is the “child” domain - the prefix you choose that indicates it’s a subsection of the larger domain - in this example, it’s ‘mail’. You can also think of the subdomain as what comes immediately after the @ symbol.

You can put anything before the @ symbol - what affects warmup and your sending reputation is the subdomain!

Last note: when you’re setting up a new subdomain, make sure it hasn’t been used elsewhere, e.g. for marketing campaigns or transactional emails. You’ll want to start your sending reputation off fresh for the best chance at great long-term deliverability.

Warmup schedule

The ideal ramp for your new domain and IP pairing includes a first send in the range of 2,000 to 5,000 recipients that gets great engagement (read: good content sent to engaged subscribers). After the first send, you should increase volume over time, sending campaigns at a regular cadence and continuing to prioritize good engagement.

Warmup schedules vary depending on list hygiene, engagement, email frequency, and content. Here’s a basic schedule we’ve found works well:

  • First send: 2,500 contacts
  • Second send: 5,000 contacts
  • Third send: 10,000 contacts
  • Fourth send: 20,000 contacts
  • Fifth send: 30,000 contacts
  • Sixth send: 45,000 contacts etc.

One caveat: we occasionally drop it down to increases of 1.5x once the send volumes cross 30,000 recipients, to be safe. This is especially important if engagement on your first few sends drops to below 20% opens (e.g. moving instead from 30,000 recipients to 45,000 to 67,000, etc.).

Related: Just Shipped: Automed IP and Domain Warmup Feature

Especially in the early days, it’s better to exclude recipients that haven’t engaged in a long time (that are very unlikely to engage in the future). Sending to unengaged recipients will disproportionately harm your reputation when you’re in the building phase, and ISPs (Gmail, Outlook) will be trained from early on to recognize your domain as sending unengaging marketing blasts, placing your emails accordingly (unfortunately, straight to spam).

Sending cadence

ISPs don’t just look at the volume of each send - they also consider the frequency of those sends to rule out “spammy” behavior. Because of this, sending every other day is much better than once every other week. We’ve seen customers have success with breaking out a larger campaign to send on multiple days.

This is where setting up solid automations from the get go gives you bonus points. An automated welcome series or new customer thank you provides a consistent amount of volume every day, on top of bulk marketing campaigns. Even better, automated emails are engaged with at a much higher rate than marketing campaigns. Remember to focus on a subject line and template that will get high opens and clicks when creating automations.

What to watch out for

Dedicated IPs

Some ESPs will offer you the option of a dedicated IP, but unless you’re sending hundreds of thousands of emails every single day, it’s unlikely that you’ll ever be able to send at a volume where you can maintain its reputation. We often see people switch to a dedicated IP and find out that it’s only a quick fix - it may initially give you great inbox placement, but without high volume daily sends, it’s almost impossible to keep up.

Engagement rates

When first warming up your domain, you need to prepare for a little bit of an adjustment period. You may not see the exact engagement rates you saw from previous subdomains (possibly lower or higher) for the first few sends. This is because it’s the first time ISPs are seeing your new subdomain - it will take a little bit of trust building (ramping up sending, at a regular cadence, to highly engaged recipients) before your engagement to shakes out to the average that you’ll see over time.

Landing in spam

In some cases, setting up a new subdomain can have your campaigns landing in spam for some subscribers during the first few sends. Don’t freak out–ISPs place emails differently for each recipient based on past behaviour and how likely they are to engage with an email.

Related: The Best Ways to Avoid the Spam Folder

This also contributes to automations being a great idea for engaging subscribers from your new subdomain, right off the bat. While new marketing emails may get filtered to spam, timely, relevant automations are much more likely to hit inbox and be engaged with.

Think of it on an individual level: if a single recipient opens and clicks on every email you send them, it will always hit the inbox. If a recipient becomes unengaged, every email you send them from there on out is more likely to end up in spam.

Wrap up

We hope this post has helped you learn something new about warming up a subdomain while thinking about deliverability in a new way. Stay tuned for more learnings on best practices that will help you build a strong long-term email strategy!