What is an email subdomain?

An email subdomain is a prefix added to your main domain name to create a separate, distinct domain for specific email sending purposes. For example, if your main domain is yourcompany.com , you might use marketing.yourcompany.com for promotional emails or transactional.yourcompany.com for operational emails.

How does a dedicated subdomain affect sender reputation?

Using a dedicated subdomain for promotional campaigns helps to isolate their sender reputation. This means that any deliverability issues, such as low engagement or spam complaints, associated with your marketing emails will primarily affect the subdomain's reputation, rather than the overall reputation of your main domain . This separation protects the deliverability of your more critical transactional or operational emails.

Do I need to warm up a new subdomain?

Yes, it is generally necessary to warm up a new subdomain. ISPs track sending history and reputation by domain (and IP address). A new subdomain has no prior sending history or established trust. You should start by sending low volumes of highly engaging emails and gradually increase the volume over several weeks. This process helps to build a positive sending reputation for the new subdomain.

What open rate indicates a deliverability problem?

While there's no fixed percentage that universally signals a deliverability problem, open rates below 10-15% for engaged subscribers might indicate an issue. However, low open rates can also be due to unengaging content, poor list hygiene, or audience fatigue, not necessarily deliverability. It's crucial to look at other metrics like click-through rates, spam complaint rates, and inbox placement tests (using seed lists) to get a complete picture. A low open rate on its own does not always mean your emails are going to spam.

Can splitting email types onto subdomains hurt overall performance?

Splitting email types onto subdomains can potentially hurt overall performance if your main domain relies on the volume and positive engagement of promotional emails to maintain its reputation. If the transactional email volume is too low to sustain a healthy reputation on its own, it might struggle after the promotional emails are moved. Assess your total sending volume and the engagement patterns across all email types before making a decision.

Should I move promotional email campaigns to a dedicated subdomain? - Sender reputation - Email deliverability - Knowledge base

The question of whether to move promotional email campaigns to a dedicated subdomain is a common one, and it touches on the core principles of email deliverability and sender reputation. Many marketers observe that promotional emails often have lower engagement rates, such as open rates (OR) and click-through rates (CTR), compared to transactional or educational content. This can lead to concerns about whether these lower-performing campaigns might negatively impact the sender reputation of the primary domain, potentially affecting the deliverability of all email types.

Understanding the nuances of how email providers assess sender reputation is crucial when making this decision. Email deliverability isn't just about avoiding the spam folder, it's about ensuring your messages consistently reach the inbox. We'll explore the strategic advantages, key considerations, and potential drawbacks of using a dedicated subdomain for your promotional email efforts, helping you make an informed choice for your email program.

Understanding sender reputation and its impact

Sender reputation is the single most important factor determining whether your emails land in the inbox or the spam folder. Internet service providers (ISPs) like

Google and

Yahoo assign a score to your sending domain and IP address based on various metrics. These include user engagement (opens, clicks, replies), spam complaints, bounces, and whether you're listed on any email blacklists or blocklists.

When all your email traffic, regardless of its nature (transactional, promotional, informational), originates from a single domain, their reputations are intertwined. If your promotional campaigns consistently generate low engagement or high complaint rates, this negative feedback can inadvertently drag down the reputation of your primary domain. This puts essential communications, like password resets or order confirmations, at risk of being filtered or delayed. The goal is to safeguard your most critical email streams from the performance fluctuations of less critical ones.

Considering the risks, it's important to understand how different email types contribute to your overall sender reputation. Transactional emails, by nature, often have high engagement because recipients are expecting them. Promotional emails, on the other hand, might be less anticipated and, if not well-targeted, can lead to lower engagement or higher unsubscribe rates. This disparity in performance is why separating them can be a prudent strategy.

The risk to your main domain

A single poorly performing promotional campaign can negatively impact your main sending domain's reputation. This can lead to all your emails, including critical transactional messages, being sent to the spam folder or even getting your domain blocklisted or blacklisted. Maintaining a robust sender reputation is vital for consistent inbox placement.

Strategic advantages of subdomains for campaigns

One of the primary benefits of using a dedicated subdomain for promotional emails is the isolation of sender reputation. By separating your marketing blasts to, for example, promo.yourdomain.com, you create a distinct sending identity for these emails. This means that if a particular promotional campaign performs poorly, it's the subdomain's reputation that takes the hit, not your main domain's. This protects your core communications, like transactional emails, from being affected.

A dedicated subdomain also allows for more precise

tracking and analytics. You can monitor the specific performance metrics (open rates, click rates, bounce rates, spam complaint rates) of your promotional campaigns without them being diluted or obscured by the performance of other email types. This granular data provides clearer insights into what's working and what's not, enabling more targeted optimization efforts.

Moreover, using separate subdomains can facilitate targeted IP and domain warming strategies. If you acquire a new list or start a new type of promotional campaign, you can gradually increase sending volume from a new subdomain without risking the established reputation of your main domain. This allows for a more controlled approach to scaling your email efforts. You can learn more about this approach from Braze's guide to email sending domains.

Single domain sending

Mixed reputation: All email types contribute to a single sender reputation, making it vulnerable to lower engagement from promotional content.
Higher risk: A single issue, like a spike in spam complaints from a marketing campaign, can affect critical transactional email deliverability.
Limited insights: Performance metrics are combined, making it harder to pinpoint specific deliverability issues for different email streams.

Dedicated subdomain sending

Reputation separation: Promotional email performance is isolated, protecting the main domain's reputation for critical communications.
Deliverability insights: Provides granular data for promotional campaigns, allowing for more precise optimization.
Risk containment: If the promotional subdomain faces issues like being blacklisted, the primary domain remains unaffected.

Key considerations for implementation

Before making the move, it is important to carefully consider several factors. One crucial aspect is email volume. A new subdomain (or IP address) needs to establish its own reputation, which requires consistent sending volume. If your promotional email volume is very low, it might not be enough to build and maintain a strong reputation on a dedicated subdomain. Conversely, if your main domain's volume is heavily reliant on promotional emails, separating them might leave the transactional domain with insufficient volume to maintain its reputation, potentially harming its deliverability.

Another critical step is warming up the new subdomain. Just like a new IP address, a new subdomain starts with no established reputation. You'll need to send emails gradually, increasing volume over time to build trust with ISPs. This warm-up process ensures that the new subdomain doesn't immediately get flagged as suspicious. Aptitude 8 provides a good guide on warming up new domains.

Finally, the technical setup is vital. You'll need to configure SPF, DKIM, and DMARC records for your new subdomain. Proper authentication is a cornerstone of good deliverability. Ensure your DNS records are correctly published to authorize your sending platform to send emails on behalf of your subdomain.

Configuring DNS for your subdomain

When setting up your promotional subdomain, you'll need to add specific DNS records. Here's an example of typical DNS records you might configure for mail.yourdomain.com using a common email service provider (ESP):

Example DNS records for email subdomainplaintext

TXT (SPF): mail.yourdomain.com TXT "v=spf1 include:esp.com ~all"
CNAME (DKIM): s1._domainkey.mail.yourdomain.com CNAME s1.domain.mail.esp.com
TXT (DMARC): _dmarc.mail.yourdomain.com TXT "v=DMARC1; p=none; rua=mailto:dmarc_reports@yourdomain.com; ruf=mailto:dmarc_forensic@yourdomain.com; fo=1;"

Always refer to your ESP's documentation for the exact records.

Weighing the potential downsides

While separating promotional campaigns to a dedicated subdomain offers many advantages, it's essential to acknowledge potential drawbacks. One concern is the division of reputation. If your main domain benefits from the high engagement of promotional emails, separating them might mean the main domain loses some of that positive volume. This could potentially make it harder for your transactional volume to stand on its own reputation, depending on your overall sending patterns.

Another consideration is increased management overhead. You'll need to manage and monitor the reputation of two separate sending identities, including configuring and maintaining SPF, DKIM, and DMARC records for both. This adds complexity to your email program, requiring more attention to ensure all aspects are properly configured and monitored. The team at

Klaviyo discusses choosing a subdomain for branded sending.

Lastly, consider the branding and user experience implications. While many recipients might not notice, a subdomain like promo.yourdomain.com might appear less direct or authoritative than simply yourdomain.com. However, the benefits to deliverability often outweigh this minor aesthetic consideration, especially if you ensure your marketing email subdomains redirect to the main website.

For more information on the trade-offs, you can refer to our guide on subdomain redirects.

Aspect	Benefits	Drawbacks
Reputation	Isolated, protecting primary domain's score.	Reputation may be divided, losing shared positive impact.
Management	Clear separation for analytics and monitoring.	Increased overhead for DNS, authentication, and monitoring.
Branding	Can tailor sender identity for specific campaign types.	Potential slight dilution of main brand recognition.
Deliverability	Protects critical emails from marketing performance issues.	Requires dedicated warm-up and consistent volume for each subdomain.

Views from the trenches

Best practices

Continuously monitor your deliverability metrics, including open rates, click-through rates, and spam complaint rates, for all your email streams.

Utilize inbox testing with seed lists to confirm where your emails are actually landing, not just relying on reported open rates.

Segment your audience appropriately and ensure your content is highly relevant to maintain strong engagement, regardless of the sending domain.

If separating, ensure both your main domain and the new subdomain have sufficient sending volume to maintain healthy reputations.

Regularly check your domain and IP reputation using tools like Google Postmaster Tools and SNDS.

Common pitfalls

Assuming low open rates automatically mean emails are going to spam; content appeal can also be a significant factor.

Separating email streams without sufficient volume on the transactional domain, potentially weakening its standing.

Failing to properly warm up a new subdomain, which can lead to immediate deliverability issues.

Neglecting to monitor the reputation of your subdomains after they are set up.

Not considering the impact on branding consistency when introducing new subdomains.

Expert tips

Focus on the quality of your email content and list hygiene first. Strong engagement often resolves perceived deliverability issues.

Test and gather data before making significant infrastructure changes to understand the actual impact.

Ensure clear authentication (SPF, DKIM, DMARC) is in place for all sending domains and subdomains.

If promotional volume is low, it might be better to keep it combined with higher-performing streams to leverage shared reputation.

A/B test different 'from' names and subject lines to optimize engagement before attributing issues solely to deliverability.

Expert view

Expert from Email Geeks says a 15-35% open rate typically suggests emails are reaching the inbox, so deliverability might not be the primary concern.

2020-08-18 - Email Geeks

Expert view

Expert from Email Geeks says if promotional mail is being delivered well, the lower engagement might indicate less compelling content rather than a deliverability problem.

2020-08-18 - Email Geeks

Making the right choice for your email program

The decision to move promotional email campaigns to a dedicated subdomain is a strategic one that depends heavily on your specific email program's needs and current performance. If your promotional emails are genuinely causing deliverability issues for your main domain, or if you require more granular control and analytics over these campaigns, then a dedicated subdomain can be an excellent solution. It offers the benefit of reputation isolation, preventing lower-engagement emails from dragging down your critical communications.

However, it's not a universal panacea. Evaluate your current open rates and other deliverability metrics carefully. If your promotional emails are already performing reasonably well and not causing noticeable deliverability problems, the added complexity and potential for dividing positive sending volume might outweigh the benefits. Always ensure you have sufficient volume for a new subdomain to establish its reputation, and be prepared for the necessary technical setup and warm-up period. Ultimately, a data-driven approach, supported by regular deliverability testing, will guide you to the best strategy for your business.