Does a subdomain inherit the reputation of its main domain?

Yes, subdomains inherit some reputation from the primary domain, but they also build their own distinct reputation based on sending practices. A good primary domain can provide a new subdomain with initial trust, but poor practices on the subdomain will quickly degrade its specific reputation.

Do I need to warm up a new subdomain for email sending?

It's best practice to warm up new subdomains gradually. This involves starting with low sending volumes and slowly increasing them over several weeks. This helps mailbox providers recognize your subdomain as a legitimate sender and build a positive reputation.

Can a bad main domain reputation still affect my subdomains?

While subdomains help isolate reputation, a very poor reputation on your main domain could still have a lingering negative effect on its subdomains. The goal of subdomains is primarily to prevent issues on one stream from damaging others, not to completely erase a root domain's negative history.

What are the key benefits of using subdomains for email?

Subdomains are beneficial for protecting your main domain, improving deliverability by isolating traffic types, and enabling more granular tracking of campaign performance. They create a clear organizational structure for your email program.

Do subdomains require separate email authentication records?

Yes, each subdomain used for sending needs its own DNS records for email authentication, including SPF, DKIM, and DMARC. These records tell receiving servers that emails from your subdomain are legitimate.

When should I use subdomains for email sending and how do they affect my reputation? - Sender reputation - Email deliverability - Knowledge base

When you're managing email sending for a business, one question that often comes up is whether to send all emails from your main domain or use subdomains. It might seem like a minor technical detail, but the choice can significantly impact how your emails perform and how recipients view your brand.

Sender reputation is the cornerstone of email deliverability. It's a score assigned by mailbox providers (like Gmail and Outlook) to your sending domain and IP addresses, indicating how trustworthy you are as a sender. A good reputation means your emails are more likely to land in the inbox, while a poor one often leads to the spam folder, or even outright rejection.

The key idea behind using subdomains is to segment your email traffic, which can be a powerful strategy for managing and protecting your sender reputation. Let's explore why and when this approach makes sense, and how it truly affects your overall email standing.

Why isolate your email streams?

The primary reason to use subdomains for email sending is to isolate the reputation of different email streams. Not all emails are created equal in terms of risk. For instance, your marketing emails, like newsletters or promotional offers, inherently carry a higher risk of complaints or low engagement compared to transactional emails, such as password resets or order confirmations.

If you send all your email types from your main domain (e.g., yourcompany.com), any deliverability issues with your marketing campaigns, such as high spam complaint rates or bounces, could negatively impact your domain's overall reputation. This in turn could cause your crucial transactional emails to also land in spam folders or be rejected, severely affecting your business operations.

Sending from the main domain

Reputation risk: All email types share one reputation. Poor performance from one stream can damage deliverability for all, including critical transactional messages.
Troubleshooting: Identifying the source of deliverability problems can be harder when all traffic is mixed.

Sending from subdomains

Reputation isolation: Marketing emails can have their own reputation (e.g., m.yourcompany.com) without jeopardizing transactional emails (e.g., t.yourcompany.com).
Enhanced tracking: Easier to monitor and manage the performance of specific email campaigns or types, allowing for more targeted optimization.

This segmentation allows you to maintain a healthy reputation for your core communications even if a less engaged marketing list experiences issues. It's a foundational step in a robust email deliverability strategy, as explained further in articles on why use email subdomains.

Understanding subdomain reputation

Subdomains develop their own sender reputation, distinct from the main domain. Mailbox providers, such as Amazon SES, often recommend this approach for managing different email types. However, this isn't a complete separation. Some level of reputation inheritance can occur, especially if the root domain has a very poor reputation, it can affect its subdomains too.

This relationship between the root domain and its subdomains is crucial for understanding. While a subdomain can build its own positive sending history, a heavily blocklisted parent domain might still cast a shadow. Conversely, a strong parent domain can provide a new subdomain with some initial trust, making the warming process a bit smoother. Understanding how domain reputation works with subdomains is key.

Blocklist isolation

One of the most significant advantages of using subdomains is their ability to limit the impact of a blocklist (or blacklist) listing. If a subdomain used for a particular email stream, like marketing, gets listed on a major email blacklist due to poor sending practices, it's less likely to affect the deliverability of emails sent from your other subdomains or your main domain.

This isolation allows you to address the issue on the specific subdomain without crippling all your email communications. It's a critical safety net for businesses that send large volumes of varied email content. You can learn more about what happens when your domain is blocklisted and how subdomains can mitigate this risk.

In essence, subdomains offer a layer of protection and control over your sending reputation. While they don't completely detach from the main domain, they provide a valuable mechanism for managing risk and optimizing deliverability for diverse email strategies.

Setting up and warming your subdomains

Setting up subdomains for email sending involves configuring DNS records like SPF, DKIM, and DMARC for each one. This ensures that the emails sent from these subdomains are properly authenticated, which is a critical factor for deliverability. While the setup might seem complex, it's a standard process and vital for maintaining email security and trust.

Once configured, new subdomains need to be warmed up. This means gradually increasing the volume of email sent over time to build a positive sending history with mailbox providers. Skipping this step can lead to immediate deliverability issues, as new, unproven sending domains are often viewed with suspicion. This is a common practice for establishing sender trustworthiness.

Email type	Recommended subdomain	Purpose
Transactional emails	t.yourdomain.com	Password resets, order confirmations, shipping updates. Critical and expected by recipients, requiring high deliverability.
Marketing emails	m.yourdomain.com	Newsletters, promotions, product announcements. Higher risk of spam complaints, so isolation protects main domain.
Sales outreach	s.yourdomain.com	Cold outreach, prospecting. Often involves higher risk due to unsolicited nature, benefits greatly from isolation.
Bounce domain	bounces.yourdomain.com	Used by ESPs for SPF alignment and handling bounced emails. Not seen by recipients.

By segmenting your email types this way, you create a clearer path for managing each stream's deliverability and can quickly identify which type of email might be causing reputation issues, allowing for faster remediation.

Strategic considerations for long-term growth

Even if your current email deliverability is excellent, planning for subdomain use as your company grows can prevent future headaches. As you expand, you might introduce new email types, work with multiple email service providers (ESPs), or launch new business units. Having a predefined subdomain strategy ensures a sensible plan is in place for these future scenarios.

This strategic foresight is more of a business decision than solely a deliverability one. It's about maintainability, ease of use, and not having to re-evaluate your domain structure every time you spin up a new email stream. Creating a policy document or a clear guideline for subdomain usage can save considerable time and effort in the long run.

Example DMARC record for a subdomainDNS

v=DMARC1; p=none; rua=mailto:dmarc_reports@yourdomain.com; ruf=mailto:dmarc_forensics@yourdomain.com; fo=1;

Ultimately, while you might not need to overhaul your current sending setup if it's performing well, proactively considering a subdomain strategy can be a strong move for future scalability and risk management. It enables you to protect your core brand reputation and ensure consistent inbox placement as your email program evolves, which is why it's a key part of segmenting email streams for better deliverability.

Views from the trenches

Best practices

Isolate different email streams on separate subdomains to protect your main brand reputation.

Always warm up new subdomains gradually to build a positive sending history with mailbox providers.

Clearly define your subdomain strategy early to ensure consistency as your email program expands.

Use subdomains for SPF alignment, particularly the bounce domain, for proper email authentication.

Common pitfalls

Sending all email types from your main domain, risking the entire domain's reputation if issues arise.

Not warming up new subdomains, which can lead to immediate filtering into spam folders.

Using 'cousin domains' that are similar but not actual subdomains, which can confuse recipients.

Ignoring the subtle reputation inheritance from the root domain, which can still impact subdomains.

Expert tips

Consider that different email service providers might require separate subdomains for various functions.

Think about whether each provider should use your primary domain for DKIM authentication or a specific subdomain.

Make subdomain decisions a part of your broader business strategy for maintainability and scalability.

There is no single 'right' subdomain strategy; it varies based on company size and specific email needs.

Expert view

Expert from Email Geeks says sharing is bad when it comes to email reputation for different streams.

2022-01-27 - Email Geeks

Marketer view

Marketer from Email Geeks says cousin domains are detrimental because they train recipients to click on misleading links and dilute brand integrity. Using a subdomain keeps branding more intact.

2022-01-27 - Email Geeks

Final thoughts on subdomains

Using subdomains for email sending is a strategic decision that offers significant benefits for managing sender reputation and ensuring deliverability. By segmenting your email traffic, you can protect your main domain from potential damage caused by riskier email types, allowing critical communications to consistently reach the inbox. While it requires careful setup and warming, the ability to isolate and monitor reputation for different streams makes it a worthwhile investment for any growing business focused on email performance.