How to warm up a domain

Perhaps you’ve started a new business, you’re going through a branding shift, or maybe you’re just adding a new stream of services or trying to separate existing ones. It’s important to update your domain to reflect those changes, but don’t forget that domain changes easily influence email. The wrong move could send your messages straight to the spam folder. 

It takes time and a little finesse for a domain’s roots to take hold, but this “warmup” process is a unique opportunity to help your brand’s deliverability thrive.

Domains that affect deliverability Domains that affect deliverability">#

So let’s talk about which domains email receivers care about. You may notice even though the examples below are pulled from a single Postmark notification, there are actually four different domains being used. The more reputations at play, the more variables introduced into your deliverability.

DKIM signing domain #

This is the domain that holds your public DKIM key, used to decrypt the DKIM signature and authenticate your message. It’s best to sign your messages with your own domain, giving you the opportunity to build your domain’s reputation faster.

DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; s=pm; d=pm.mtasv.net; h=Message-ID:MIME-Version:From:To:Date:Subject:Content-Type; bh=SL7rCnlli8A9zsnT4JjD6bAHzFs=; b=uE5Y5PlSBOCGIaVxf7IeN/9Fe+iNSyOu/Ly0d5Q/WWPRDd3q6RrRA7f8kOrxv/JcVNijEeAIjN3CeyNmx1ACEMcmVoGvNCdLdhiMPIQTh1DODLTR3E2nzJgzvbwAe4gkqdnSG+x1DobA+lhKbcfKAAMDkxO1pV08iaNY44ytQqI=

Return-Path domain #

This is the domain that bounce responses are sent to, but it’s also used by receivers for SPF authentication. Again to build your reputation faster, it's recommend that you have a custom Return-Path that matches your domain.

Return-Path: <pm_bounces@pmbounces.postmarkapp.com>

From/reply address #

This is the “friendly” address we see directly in our inboxes, which often matches the domain used in the reply-to address. It should clearly identify your brand to recipients, so be sure to encourage them to add it to their contact list for improved deliverability. It's also recommended that you add a DMARC policy to this domain, which in combination with custom DKIM and Return-Path, helps protect your domain’s hard-built reputation.

From: "Postmark" <support@postmarkapp.com>

URL content #

These are the links in the content of your message itself, including any third party link-tracking, short URLs, and file hosting. In general, we see URLs negatively affect delivery only when they’re observed to have some deceptive or malicious purpose. It pays to be mindful which third-parties are linked in your content. 

<a href="https://wildbit.com">Wildbit</a> Philadelphia, PA, 19106

Working with subdomains #

A little-known fact is that subdomains develop their own reputations too. Think of them as branches of a tree. Sure, the primary organizational domain controls their ultimate fate, but they each develop separately with varying strength. Subdomains are the best way to keep your branding consistent while protecting the deliverability of your various mail streams. 

For example, if you send transactional content and promotional content, be sure to associate each with a unique subdomain using custom DKIM and Return-Path. Now it’s much less likely the wrong bulk send can affect deliverability for those most important alerts that keep your app functional. 

As with any reputation, it isn’t created out of thin air. A new subdomain still needs to be warmed up with receivers, slowly increasing the number of messages sent. 

Planning the warmup #

How do you warm up a domain or subdomain? The first step is examining who you’re sending to and how much. That means knowing how much you’re sending to Gmail recipients, Yahoo, AOL, Microsoft domains, and so on at any given time. The more segmented by receiver your list is, the better.

Now start your volume to each of these receivers very low, usually around 100-500 messages to each receiver the first couple of days. In the beginning, you can generally try doubling your volume each day. Once that volume becomes more substantial, however, grow your audience by only 20-50% each day to accommodate for any sudden issues with complaints or bounces. 

Of course, never increase your volume until you’ve looked at your messages’ performance by receiver. If engagement and bounce rates seem normal, you’re likely safe to increase the next day’s volume. If you’re seeing some behavior that suggests deliverability is suffering, however, decrease your volume by 25-30% until metrics begin to normalize. #Protip: If you’re able to target the most engaged recipients first, you’ll be establishing a good reputation faster and the entire warmup process will go much smoother.

Keep in mind that each of these receivers has a different threshold for how much mail they’ll accept from a new domain, and that threshold is dependent on a lot of variables. No single warmup schedule works for everyone, but most can expect their domain to have an established reputation and dependable full-volume deliverability in 3-6 weeks.


Domain reputation is your most valuable asset in email deliverability. IPs change and templates are redesigned, but the domain has a growing history which more than ever determines your fate in the inbox. By starting off right, you can quickly build a reputation that will help safeguard your deliverability wherever you go.


Still have questions?

  • Ashley Harpp Ashley
  • Dana Chaby Dana

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