May 30, 2022

Email subdomain best practices for deliverability

Best practices for email subdomains improving deliverability. Using a subdomain is becoming popular for email marketing our guide shows why.

Email subdomain best practices for deliverability

Email subdomain best practices for deliverability 

You will have seen email subdomains are more commonly being used on the sales emails you receive and even for general email operations across different departments. 

This aspect of email marketing set-up, which is quickly becoming a best practice for deliverability, emerged due to the increasing challenges marketers and salespeople face when trying to make sure their emails reach the primary inbox, and are not filtered automatically by ISPs into spam, unfocused or promotional folders. 

Simply put, using a subdomain, rather than your core domain, allows you to have greater visibility on the sender reputation of the domain which is being used to contact prospective customers, and decreases the overall risk of using an outbound strategy.

Want best practices on how to implement and set up your email subdomain? We’ll outline the following principles and examples:

What is a subdomain?

All emails are sent from a domain, this is why something is always written after the @ symbol of an email.

If you’re a business user, emails will be sent on the domain purchased by your business and this is commonly the main domain on your website (for example, in our case). By default, when you set up email hosting, messages will be sent from this main domain with the address you create. But, there are other options…

A subdomain is an iterated version of the main domain you have purchased in the first instance, (you can consider it a child of the main domain). A breakdown of the different aspects which make up a working email is outlined below (with a subdomain included):

Email subdomain example

From the above example, you’ll see subdomains inside an email format can be any word/letter of your choice written before the exact name of a valid domain which your business owns. The subdomain and the main domain are separated by a dot, and in the case above the subdomain is ‘’, whereas the main domain is just ‘’.

Email addresses created on subdomains and your main domain, can both be used at the same time to send and receive emails separately. 

Why subdomains are used with marketing emails

The principal reason subdomains are used for email marketing is because utilizing a subdomain separates the sender reputation of your core domain from email marketing activities. (We’ve written a separate article explaining sender reputation which you can check out if you’re unsure what this means.)

Separating the sender reputation of your core domain may seem unnecessary when you initially consider it - but, leaders in the field of marketing are doing it. This is because, as you scale any outbound strategy - increasing the control you have over deliverability and decreasing the risk of the approach becomes more valuable than simplicity. 

Seeing as subdomains have individual sender reputation scores, using one means you can avoid the risk of outbound emails negatively impacting the deliverability of your emails to current customers. The same goes for other operations, for example, transactional emails may historically have low engagement (as contacts rarely need to respond to them) and therefore, to avoid this low engagement impacting the deliverability of your marketing emails, you can conduct that transactional activity on a different subdomain.

It’s less risky for your business overall, to do email through a subdomain - as the results/sentiment associated with one particular department's emails do not have a knock-on effect on the deliverability of another department's emails.

If anything ever goes wrong over email (no one is perfect..let’s be honest), using subdomains also means it’s easier to limit the impact of the error, or in extreme cases wipe the slate clean and start using a new subdomain which will have a different sender reputation. Whereas, if something goes wrong (like a bad mail merge) on your core domain, you’re unlikely to be able to hit the reset button without changing your website and migrating your technology systems for a new domain across the board, which can lead to a huge disruption. 

Finally from an analytics perspective, if you have different subdomains for different operations, then you can also more easily compare the impact of certain campaigns or approaches on sender reputation. This is valuable for businesses which are focused on sending long term sustainable campaigns, because any initiatives which cause spam/deliverability issues, can be easily identified and adapted accordingly. 

How email subdomains are commonly implemented

Subdomains are typically implemented and assigned to different sending operations.

The simplest way to start using subdomains is to separate your cold outreach and follow-up to inbound contacts across two different subdomains. 

Many businesses also create unique subdomains for the automatic sending which is conducted by each department, while still using the company's root domain for each individual's email account - where they will be sending individual emails never cold outreach (as there is a specific subdomain for the cold outreach).

In practice, implementing the above usually resembles the following structure:

  1. The internal company domain being used for day to day operations by everyone is:

  2. Users on the sales team doing outbound prospecting have accounts on a specific subdomain such as:

  3. The marketing teams subdomain for the newsletter is:

When you are ready to add a subdomain, you’ll need to add a secondary domain to your normal inboxes so the address can be used naturally as email senders. Google provides documentation on setting up a subdomain (referring to the subdomain as a ‘secondary domain’) available here. Make sure to not set up the accounts in your G Suite as ‘alternative domains’ as these accounts are aliases, and using alias accounts goes against deliverability best practice.  Implementing subdomains for Microsoft mailboxes is possible by following their documentation here and updating your DNS records accordingly.  

Examples and subdomain ideas

You’ll probably recall seeing subdomains used in email campaigns you’ve personally received, but, here are five examples of some of the most well-known brands using them over email.

Seeing as you have free reign to create the name of your subdomain, this list should help to show you what is common practice for naming a subdomain. (for deliverability, we’d generally advise the more ‘normal’ and widely used a subdomain naming structure, the better)

1. Apple uses the ‘email.’ subdomain to communicate with their business customers in specific segments:

Apple email with subdomain

2. Gong used the ‘.talk’ subdomain to communicate with inbound sign-ups:

Gong email with subdomain

3. Allbirds has the ‘mail.’ Subdomain for their newsletter and first email after form fill:

Allbirds email with subdomain

4. Asana uses the ‘.research’ subdomain specifically for their customer success surveys:

Asana email with subdomain

5. Segment (Twillio) uses the ‘e.’ subdomain for their marketing emails. Using a single letter is slightly less common than a using a full word like the other examples:

Segment email with subdomain

Some honourable mentions for subdomain naming which are not listed above, but are worth considering are as follows: ‘hello.’, ‘chat.’’, ‘news.’, ‘blog.’, ‘learn.’ and ‘app.’. 

Warming up and monitoring a subdomain

Once you’ve created a subdomain then you’ll want to make sure that the sending which happens through it is effective. This means building a strong reputation and analysing the subdomain using a warm-up process with inbox placement monitoring.

The process of warming up an email essentially, means starting activity on the subdomain in a slow and deliberate manner - so that email providers associate high-quality email activity with the new domain, which leads to your emails landing in the primary inbox, rather than spam or promotion folders.

Strategically the best practice on how to conduct this involves 3 steps:

1. Identify contacts who have historically engaged with your emails the most. (opens, clicks and replies). Then these contacts should be engaged during the initial period of using your new subdomain in order to provide higher engagement. Which generally means emailing a list of historically engaged contacts before others. 

2. Augment the new subdomain’s engagement using an email warm-up tool. This tool should automatically provide additional replies and general engagement across the domain, which will help you reach and maintain a high sender reputation in the long term. 

3. Increase your overall sending volume on the new domain slowly. As email providers hate spikes in sending activity - you should steadily increase the volume you send over a 30-60 day period.

As well as the above, before you start email activity you should ensure you have completed each of the items on our checklist. This will help make sure there are no technical issues with the way you’ve set up your subdomain which could impact deliverability.

Should I send from a completely different domain?

Using a completely separate domain name for a specific type of email has the same strategic benefits as using a subdomain, however, the downside of this approach is brand confusion.

Generally speaking, if you’re contacting someone through a domain which has a different name or TLD (domain ending) to the main one associated with your brand, website and company - The recipient could be more inclined to find the email untrustworthy, and is therefore less likely to engage. 

The only use-cases we’ve found where completely different domains make sense, is when your email activity is ‘high risk’, this means sending operations like the following use cases:
- Fully automated cold emails.
- Verification emails.
- Outreach to free emails and catch-all servers.

It’s important to note, that when it comes to reaching your marketing objectives, avoiding any form of high-risk sending is unrealistic. Therefore, your focus should be on managing the higher risk sending operations effectively and minimizing their potential impact on your sender reputation.

With high-risk operations, it’s becoming common to manage more than one subdomain/domain, because using your core domain forever with in higher risk sending activities can be detrimental to sender reputation and core business operations. Therefore, you will want to keep in mind that using a separate domain altogether is likely to be an ‘as well as’, rather than an ‘instead of’ approach in the long term. 

Email subdomain best practices checklist

Think you’re ready to get started using a subdomain for sending?

Here’s a quick list of checks to conduct on the new subdomain so you’re set up for a successful implementation:

  • SPF, DKIM and DMARC protocols are set up on your new subdomain.

  • The subdomain has email accounts which can both send and receive emails.

  • You have chosen a standard name based on the options we provided, and aren’t using something which could be perceived as a spammy or unusual keyword.

  • The accounts you have set up on the subdomain for communications are real email accounts not ‘alias users’ or ‘alternative email addresses’.

  • You’ve connected and started a warm-up system on the subdomain.

  • You will steadily increase your sending over a 30 to 60 day period rather than starting at your target volume right away.

  • You are able to monitor the subdomain's sender reputation over time, in comparison to other subdomains and your core domain. 

  • The systems you use to automate emails are connected exclusively to the relevant subdomains, not your core domain anymore.