Why use subdomains for email marketing deliverability?

Key findings

• Reputation isolation: Subdomains allow you to build and maintain separate sender reputations for different email types. This protects your main domain from negative impacts should one email stream experience deliverability issues, like blocklisting.
• Enhanced control: They provide more granular control over email authentication protocols, including SPF, DKIM, and DMARC. This is crucial for proper configuration and avoiding common pitfalls such as SPF lookup limits.
• Improved deliverability: Isolating marketing traffic, which often has different engagement metrics and sending patterns, helps inbox providers better assess and route your mail, leading to improved inbox placement. Read more about improving deliverability.
• Easier monitoring: With separate reputations, it's easier to monitor specific sending practices and their impact on deliverability. This simplifies troubleshooting and allows for more targeted adjustments, as highlighted by Mailgun.

Key considerations

• Domain authentication: Each subdomain requires its own proper SPF, DKIM, and DMARC setup to ensure emails are authenticated correctly. Incorrect setup can lead to deliverability issues. See if a subdomain needs its own SPF record.
• Warm-up period: New subdomains, like new IPs, require a warm-up period to build a positive sending reputation with internet service providers (ISPs). Starting with low volumes and gradually increasing helps establish trust.
• Brand consistency: While subdomains offer separation, ensure the chosen subdomain names maintain brand recognition and trust with recipients to avoid confusion or appearing suspicious.
• Avoiding cousin domains: It is generally advised to avoid cousin or look-alike domains that could be mistaken for phishing attempts, even if they are legitimate.

Key opinions

• Preventing reputational damage: Marketers frequently emphasize that using a subdomain for bulk or marketing emails prevents any deliverability issues from affecting the main corporate domain and its essential communications.
• Strategic isolation: Many view subdomains as a critical tool for isolating different types of email traffic. This segmentation allows for tailored sending practices and reputation management per email category.
• Facilitating DMARC monitoring: Some marketers find that using separate domains or subdomains, especially for specific campaigns, can make DMARC monitoring easier, particularly with lower email volumes. Read more on understanding DMARC reports.
• Security considerations: For sensitive or high-profile communications, some marketers even consider entirely different domains for enhanced security, although subdomains are generally sufficient for reputation separation.

Key considerations

• Marketing team impact: There's a strong sentiment that relying on the root domain for bulk mail can lead to severe corporate disruption if marketing efforts go awry. This emphasizes the need for separation.
• Brand visibility vs. protection: While marketers want their brand visible, the consensus is that the protection offered by subdomains outweighs the slight reduction in root domain exposure for bulk sends.
• Avoid deceptive tactics: Some specific use cases, like political campaigns, might involve hiding the direct connection to the main business domain for security or strategic reasons, which requires careful implementation to avoid appearing deceptive.
• Vendor advice: Marketers frequently receive advice from vendors to switch to subdomains for improved deliverability, and generally, they find this advice to be sound. Learn more about why vendors recommend subdomains.

Key opinions

• Authentication control: Experts emphasize that subdomains allow for more granular control over authentication settings like SPF, DKIM, and DMARC. This helps in avoiding common issues such as exceeding SPF lookup limits.
• Reputation separation: The primary benefit cited is the ability to develop a largely separate reputation for subdomains. This significantly lowers the risk of poor sending practices on a marketing subdomain affecting the reputation of the root organizational domain.
• Business imperative: It is considered a fundamental business necessity to never use the same domain for corporate mail and bulk mail. Failing to do so can lead to severe operational paralysis if marketing efforts result in blocklists or low reputation.
• Sufficient separation: Subdomains are generally considered sufficient for achieving the necessary separation and control, without requiring entirely different top-level domains, which can be less brand-friendly.

Key considerations

• Avoiding cousin domains: Experts strongly advise against using cousin or look-alike domains due to their potential for misuse and increased suspicion from ISPs.
• Security and brand recognition: Subdomains offer the same level of control and security as completely different domains, but with the added benefit of maintaining brand recognition and reducing phishing concerns associated with unfamiliar domains.
• Impact of marketing activity: If marketing teams are prone to aggressive sending or other practices that could harm reputation, using a subdomain acts as a vital buffer, preventing negative consequences from affecting the entire organization's email infrastructure. Discover more on what happens when your domain is blocklisted.
• Simplified management: Experts acknowledge that while subdomains add a layer of complexity to initial setup, they simplify ongoing management and troubleshooting by segmenting email flows and their respective reputations. Read a detailed view from Mailgun on email subdomains.

Key findings

• Domain reputation segmentation: Documentation often emphasizes that subdomains allow for the separation of reputation, meaning that if one subdomain experiences issues, the primary domain and other subdomains remain unaffected.
• Improved sender identity: By using subdomains, senders can better clarify the purpose of their emails to inbox providers, which helps in consistent engagement levels across different recipient groups.
• Authentication flexibility: Technical guides point out that each subdomain can have its own SPF, DKIM, and DMARC records, providing greater flexibility and control over email authentication. Learn more about DMARC, SPF, and DKIM.
• Mitigation of blocklist impact: Should a subdomain be listed on a blocklist, the impact is contained to that specific subdomain, preventing the entire primary domain from being affected. This is a key protective measure.

Key considerations

• Consistent brand identity: Documentation advises that sticking with clear and consistent subdomains helps reinforce brand identity and builds trust with both inbox providers and recipients, as mentioned by Resend.
• Warm-up for new subdomains: Like new IPs, new subdomains require a careful warm-up process to establish a good sender reputation before sending high volumes. Learn more about subdomain warm-up.
• Careful segmentation: While subdomains offer benefits, documentation implies that effective segmentation depends on the nature of the email content (e.g., transactional, promotional, notifications) and audience engagement.