Is it always necessary to use separate subdomains for marketing and transactional emails?

Yes, it is generally recommended. Separate subdomains allow you to isolate the sender reputation of your high-engagement transactional emails from your potentially lower-engagement marketing emails. This protects the deliverability of critical communications if your marketing efforts encounter issues like higher spam complaints or bounces.

What are the main benefits of separating email types by subdomain?

The primary benefit is reputation isolation . If one stream, particularly marketing, experiences deliverability problems (e.g., high spam complaints), it won't negatively impact the other stream. It also provides clearer analytics for each email type and helps Mailbox Providers classify your emails correctly.

Do I need to set up SPF, DKIM, and DMARC for each separate subdomain?

Yes, you need to set up SPF, DKIM, and DMARC records for each subdomain individually . These authentication protocols are domain-specific, so configuring them for each subdomain ensures proper email validation and helps build their distinct reputations.

How much email volume do I need to justify using separate subdomains?

Ideally, you should have enough volume on both subdomains for Mailbox Providers to assess and build a reliable reputation. While there's no fixed number, consistent sending in the thousands of emails per month for each stream is often sufficient. Very low volume might make it harder to establish a strong, distinct reputation.

Does using separate subdomains add too much complexity to email management?

While it adds an initial setup layer, most Email Service Providers (ESPs) simplify the process of configuring DNS records for subdomains. The long-term benefits in terms of improved deliverability and risk mitigation generally outweigh the added complexity.

Should I use separate subdomains for marketing and transactional emails? - Technical - Email deliverability - Knowledge base

The question of whether to use separate subdomains for marketing and transactional emails is a common one, and it's something I've seen debated often within the email community. My strong recommendation, based on years of observing email deliverability, is yes, you should absolutely use distinct subdomains for these different types of email. It's a foundational best practice for maintaining a healthy sender reputation and ensuring your critical messages reach the inbox.

Different email types serve different purposes and, crucially, have vastly different engagement metrics. Transactional emails, like password resets, order confirmations, and shipping notifications, are typically highly anticipated and have high open and click-through rates. Marketing emails, on the other hand, while essential for growth, often have lower engagement, higher complaint rates, and are more susceptible to being marked as spam or promotions.

Mixing these streams on a single domain means that the poorer performance of marketing emails can negatively impact the deliverability of your vital transactional messages. This separation is key to protecting your brand's core communication channels.

Benefits of separation

The primary reason for segmenting your email streams via subdomains is to protect your sender reputation. Every domain you send from develops a reputation with Mailbox Providers (MBPs) such as Gmail, Outlook, and Yahoo. This reputation is a critical factor in whether your emails land in the inbox, the spam folder, or are blocked entirely. When you send both marketing and transactional emails from the same domain (or root domain), their reputations are intertwined.

If your marketing emails experience high bounce rates, low engagement, or worse, elevated spam complaints, this negative feedback directly impacts the reputation of your primary sending domain. This, in turn, can cause your crucial transactional emails, which users expect and need, to also face deliverability issues.

By using separate subdomains, you create distinct reputations. For example, transactional emails sent from mail.yourdomain.com can maintain a pristine reputation due to high engagement. Meanwhile, marketing emails from marketing.yourdomain.com can absorb any potential negative feedback without affecting the deliverability of your transactional messages. This strategic separation helps ensure that even if your marketing efforts hit a snag, your essential communications remain unaffected.

Transactional emails

These are expected, timely, and usually high-priority messages. Their delivery is crucial for user experience and business operations. Examples include password resets, order confirmations, shipping updates, and account alerts. Users typically interact positively with these emails, leading to high open rates and low complaint rates, which builds a strong sender reputation.

Marketing emails

These emails are promotional and often unsolicited, even if the recipient opted in. They are designed to drive sales, engagement, or provide information not critical to immediate user action. Examples include newsletters, promotional offers, and product updates. These often have lower engagement rates and higher complaint rates, which can negatively impact sender reputation.

This method is widely considered best practice, helping to mitigate risk by preventing a drop in marketing email reputation from affecting your mission-critical transactional messages. To learn more about how reputation works, check out our guide on how email blacklists actually work.

Technical setup for subdomains

Setting up separate subdomains for your email streams involves a few key technical steps, primarily in your Domain Name System (DNS) records. You'll need to configure SPF, DKIM, and DMARC records for each subdomain. While the specific records will depend on your Email Service Provider (ESP), the general principle is the same.

For SPF, you'll publish a TXT record for each subdomain that specifies which mail servers are authorized to send email on its behalf. DKIM involves adding a CNAME record that points to a public key provided by your ESP, enabling recipients to verify the email's authenticity. DMARC, crucial for enforcement, will also require a TXT record for each subdomain, allowing you to monitor and control how unauthenticated emails are handled.

Consider naming your subdomains clearly, such as mg.yourdomain.com for marketing and tx.yourdomain.com for transactional. This clarity helps you and MBPs distinguish between email types. It's not uncommon for businesses to use separate IP addresses as well, further isolating the sending infrastructure. Our guide on whether to use separate IPs or domains delves deeper into this.

SPF Record ExampleDNS

v=spf1 include:_spf.yourdomain.com ~all

Important authentication details

SPF (Sender Policy Framework): Specifies which mail servers are authorized to send email on behalf of your subdomain. Each subdomain needs its own SPF record.
DKIM (DomainKeys Identified Mail): Adds a digital signature to your emails, allowing recipients to verify that the email has not been tampered with. Your ESP will provide a unique DKIM record for each subdomain.
DMARC (Domain-based Message Authentication, Reporting & Conformance): Builds on SPF and DKIM, giving you control over what happens to emails that fail authentication. Set up a DMARC record for each subdomain, starting with a relaxed policy (p=none) and gradually moving to quarantine or reject as you gain confidence.

Managing subdomain health

Once you've set up your separate subdomains, the work isn't over. Ongoing management is crucial to maintain their health and ensure optimal deliverability. You need to actively monitor the performance of each subdomain independently. This includes tracking key metrics like open rates, click-through rates, bounce rates, and crucially, spam complaint rates for each email stream.

Mailbox Providers (MBPs) often offer tools for senders to monitor their reputation. For instance, Google Postmaster Tools provides valuable insights into your domain and IP reputation, spam rates, and delivery errors. By segmenting your emails to different subdomains, you can get granular data for each type, making it easier to pinpoint and address specific deliverability issues. For example, if your marketing subdomain's spam rate spikes, you can address that without disrupting your transactional emails.

Additionally, actively managing your sending lists and email content is vital. Regularly clean your lists to remove inactive or invalid addresses, which can lead to bounces or spam traps, potentially landing you on a blacklist (or blocklist). Ensure your content aligns with user expectations for each email type. Transactional emails should be concise and direct, while marketing emails should provide clear value and an easy unsubscribe option. This continuous effort will contribute significantly to your overall email deliverability and protect your main domain.

Metric	Transactional Subdomain Focus	Marketing Subdomain Focus
Open rate	Aim for very high rates (often 70-90%+) due to user expectation.	Fluctuates more, monitor trends. Lower is expected (20-40% typically).
Click-through rate	High rates, as emails often contain critical action links.	Varies by campaign, focus on specific call-to-action performance.
Spam complaint rate	Should be exceptionally low (ideally near 0%). Crucial for reputation.	Expect higher, but keep below industry thresholds (e.g., 0.1%).
Bounce rate	Keep low by maintaining a clean, validated list of active users.	Manage by regularly cleaning lists, especially after campaigns.

Addressing common concerns

A common concern when considering separate subdomains, especially for smaller senders, is whether there's sufficient email volume to build and maintain a good reputation on each. It's true that some volume is needed for Mailbox Providers to assess your sending patterns accurately. If a subdomain sends too little email, it might not establish a clear reputation, potentially leading to less predictable deliverability.

However, for most businesses with active transactional email flows and consistent marketing campaigns, there will be enough volume. The threshold for sufficient volume can vary greatly depending on the target MBP and the specific sending patterns. What might be enough for one provider could be different for another. Generally, if you're sending in the thousands of emails monthly for each stream, you should be able to build distinct reputations. You can refer to our article on how subdomains improve deliverability for more insights.

Another consideration is managing the complexity. While setting up multiple subdomains adds an initial layer of DNS configuration, the long-term benefits in terms of deliverability and risk mitigation far outweigh the small increase in administrative effort. Most modern ESPs make this process relatively straightforward, providing clear instructions for DNS records. Ultimately, the goal is to improve your overall email deliverability, and subdomain separation is a powerful tool to achieve that.

Views from the trenches

Best practices

Always set up proper SPF, DKIM, and DMARC records for each subdomain to ensure authentication.

Consistently send adequate volume from each subdomain to build a reliable and distinct sender reputation.

Monitor deliverability metrics, like open rates and spam complaints, separately for each subdomain.

Common pitfalls

Not having enough volume on a subdomain, which can make it harder for MBPs to establish its reputation.

Failing to implement all necessary email authentication records for each subdomain.

Ignoring complaint rates on marketing subdomains, which can still lead to broader domain issues if not managed.

Expert tips

Use clear and descriptive subdomain names to easily distinguish between email types.

Regularly clean email lists for each segment to maintain high engagement and avoid spam traps.

Gradually ramp up sending volume on new subdomains to warm them up properly with MBPs.

Expert view

Expert from Email Geeks says: Separating mail streams with different subdomains and matching DKIM signing is a good practice.

2022-04-27 - Email Geeks

Marketer view

Marketer from Email Geeks says: Separating mail streams by using different subdomains is a widely accepted and beneficial practice.

2022-04-27 - Email Geeks

Key takeaway

Using separate subdomains for marketing and transactional emails is a strategic move that pays dividends in email deliverability and overall brand protection. It allows you to isolate the reputation of your essential transactional messages from the inherently more volatile reputation of marketing emails, ensuring your critical communications always reach their intended recipients.

While it requires careful setup of DNS records and ongoing monitoring, the benefits of enhanced deliverability, clearer analytics, and reduced risk make it a worthwhile investment for any business serious about its email program.