Should I use separate email subdomains for transactional and promotional emails, and how does engagement affect this?

The overwhelming consensus is that using separate subdomains for transactional and promotional emails is a best practice to protect sender reputation and improve deliverability. By isolating email streams, issues with one subdomain (e.g., low engagement with promotional emails) are less likely to negatively impact the deliverability of critical transactional emails. Technical documentation from Google, SparkPost, Microsoft and RFC Editor supports this approach, emphasizing that subdomains are treated as separate entities, allowing for independent reputation management. However, some experts caution that shared infrastructure, such as IP addresses, can still lead to reputation bleeding between subdomains and the main domain, highlighting the importance of understanding how mailbox providers handle subdomain reputation and potentially using separate sending IPs for transactional emails. Managing data quality and addressing issues like invalid addresses are also key to maintaining a positive sender reputation.

Key findings

• Reputation Isolation: Using separate subdomains isolates sender reputation, protecting transactional emails from issues affecting promotional emails.
• Improved Deliverability: Segmenting email traffic by subdomain improves overall deliverability rates, particularly for transactional emails.
• Control Over Reputation: Subdomains provide greater control over sender reputation management, allowing for the isolation and resolution of deliverability problems.
• Technical Support: Technical documentation from Google, SparkPost, Microsoft and RFC Editor supports the practice of using subdomains to separate email traffic and isolate sender reputation.

Key considerations

• Infrastructure Sharing: Shared infrastructure, like IP addresses, can cause reputation bleeding between subdomains, potentially negating the benefits of separation.
• Reputation Management Overhead: Creating and maintaining separate subdomains requires additional effort in managing and monitoring their individual reputations.
• Mailbox Provider Variations: It's important to understand how different mailbox providers handle subdomain reputation, as their policies and practices can vary.
• Data Quality Importance: Maintaining high data quality (e.g., validating email addresses) is crucial for overall sender reputation, regardless of subdomain usage.

The consensus is that using separate subdomains for transactional and promotional emails is a good practice to protect sender reputation and improve deliverability. Separating email streams helps isolate reputation issues; low engagement or problems with promotional emails are less likely to affect the delivery of critical transactional emails. However, some experts caution that shared infrastructure (like IP addresses) can still lead to reputation bleeding between subdomains.

Key opinions

• Reputation Isolation: Separate subdomains help isolate sender reputation, preventing issues with promotional emails from impacting transactional email deliverability.
• Deliverability Improvement: Segmenting transactional and promotional emails onto different subdomains improves overall deliverability.
• Control Over Reputation: Separating subdomains gives more control over sender reputation, allowing for the isolation and management of deliverability issues.
• Protection of Core Domain: Subdomains protect the core domain's reputation, minimizing the impact of marketing campaign issues.

Key considerations

• Infrastructure Sharing: Shared infrastructure, such as IP addresses, can cause reputation bleeding between subdomains.
• Reputation Management: Creating new subdomains requires managing their individual reputation.
• Data Quality: Addressing data quality (e.g., invalid addresses) is crucial for sender reputation.
• Engagement Balancing: High engagement campaigns can balance out the metrics for lower engagement ones.

Experts agree that separating transactional emails onto a separate subdomain improves sender reputation. However, it's critical to consider the impact of shared infrastructure (like IP addresses). A poor reputation on one subdomain can negatively affect others and the main domain if they share IP addresses. Thus, some experts suggest using a separate sending IP for transactional emails.

Key opinions

• Subdomain for Transactional Emails: Sending transactional emails from a separate subdomain improves sender reputation.
• Separate IP for Transactional Emails: Using a separate sending IP for transactional emails further enhances sender reputation.

Key considerations

• Shared Infrastructure: Shared IP addresses can cause reputation bleeding between subdomains and the main domain.
• Mailbox Provider Handling: Understanding how mailbox providers handle subdomain reputation is crucial for your sending context.

Technical documentation supports using separate subdomains for different email streams (transactional vs. promotional). Google, SparkPost, RFC, and Microsoft all emphasize that subdomains are treated as separate entities, enabling the isolation of sender reputation. A key benefit is preventing poor engagement from one subdomain from negatively impacting the deliverability of others.

Key findings

• Reputation Isolation: Subdomains allow for isolating the reputation of different email streams.
• Segmented Email Traffic: Subdomains are useful for segmenting different types of email traffic.
• Independent Entities: Subdomains are treated as separate entities from a technical perspective.
• Improved Deliverability: Using subdomains improves deliverability for critical transactional emails by protecting them from negative impacts on promotional emails.

Key considerations