Summary
The consensus across experts, marketers, and documentation sources is that subdomain reputation significantly impacts core domain reputation. While subdomains offer segmentation and a degree of isolation, issues on a subdomain can negatively affect overall deliverability. Mailbox providers vary in their methods of assessing domain reputation, some aggregating subdomain data while others maintain separation or use weighted metrics. Key to maintaining a positive domain reputation is consistently adhering to good sending practices across all subdomains and diligently monitoring their performance. Complete isolation is difficult without dedicated IPs, and blocklists may target the parent domain regardless of subdomain reputation.
Key findings
- Reputation Interdependence: Subdomain reputation directly affects the parent domain's deliverability and sender reputation.
- MBP Variance: Mailbox providers differ in how they assess domain reputation, leading to varied impacts.
- Limited Isolation: Subdomains offer limited isolation; poor practices inevitably impact the core domain.
- Importance of Monitoring: Constant monitoring of subdomain performance is crucial to prevent reputational damage.
Key considerations
- Implement Best Practices: Enforce consistent and ethical sending practices across all subdomains.
- Monitor Subdomain Health: Regularly assess subdomain health metrics and promptly address any anomalies.
- Consider Domain Separation: Evaluate the benefits of separate domains for critical email streams to isolate reputation.
- Authentication Protocols: Use strong authentication methods (DKIM, SPF, DMARC) to protect the entire email ecosystem.
What email marketers say
9 marketer opinions
The reputation of subdomains significantly impacts the core domain's reputation. While subdomains offer segmentation and a degree of isolation, poor sending practices or issues on a subdomain can negatively affect the overall domain's deliverability. Mailbox providers vary in how they assess domain reputation, some rolling up subdomain data, others keeping them separate or using weighted data. Maintaining good sending practices across all subdomains is crucial, as is careful monitoring to prevent damage to the core domain.
Key opinions
- Subdomain Impact: Subdomains influence the core domain's reputation; poor practices degrade overall deliverability.
- Provider Variance: Mailbox providers handle subdomain reputation differently (rollup, separate, weighted).
- Isolation Limited: Subdomains offer some isolation, but a compromised subdomain harms the entire domain.
- Segmentation: Subdomains are useful for segmenting sending practices but require careful management.
Key considerations
- Monitor Performance: Carefully monitor subdomain performance to prevent damage to the core domain reputation.
- Sending Practices: Maintain good sending practices across all subdomains to ensure optimal deliverability.
- Authentication: Consider using DKIM with separate domains/selectors for each publisher to isolate reputation.
- Individual Domains: Using individual or dedicated domains with unique authentication is beneficial for senders.
Marketer view
Marketer from Email Geeks explains that it depends on the receiver (Mailbox Provider) and how they've configured their domain reputation systems, as some roll it all up, some keep them separate, while others use the data to inform the "core domain" with weighted data.
16 Nov 2022 - Email Geeks
Marketer view
Email marketer from Reddit explains that subdomains offer some level of isolation, however a really bad subdomain will affect the overall domain reputation. Maintaining good sending practices on all subdomains is very important.
23 Jun 2022 - Reddit
What the experts say
5 expert opinions
Experts agree that subdomain reputation significantly affects the core domain's deliverability. Subdomains create their own reputations which then influence the parent domain's overall reputation, often weighted by volume. Complete isolation is difficult to achieve without dedicated IPs. Poor sending practices on subdomains can negatively impact the entire domain's ability to reach inboxes, and blocklists often target the parent domain regardless of subdomain reputation. Maintaining good sending habits across all subdomains and closely monitoring them is critical.
Key opinions
- Direct Impact: Subdomain reputation directly impacts the parent domain's deliverability.
- Reputation Cycle: Subdomains have their own reputations, affecting and being affected by the parent domain.
- Blocklisting: Blocklists often target the parent domain, regardless of subdomain reputation.
- Limited Isolation: Complete isolation of subdomain reputation is nearly impossible without dedicated IPs.
Key considerations
- Good Habits: Maintain good sending habits across all subdomains.
- Monitoring: Closely monitor subdomains for sending reputation issues.
- Domain Separation: Consider using separate domains to avoid shared reputation issues.
- Authentication: Implement strong email authentication across all domains and subdomains.
Expert view
Expert from Email Geeks explains that subdomains create their own reputation, which is primary for that subdomain. The parent domain reputation is a mix of all subdomains' reputations, weighted by volume. Reputation drips down from the parent to subdomains and up from subdomains to the parent.
24 Jan 2024 - Email Geeks
Expert view
Expert from Word to the Wise shares that subdomains can help in separating reputation, but a poorly managed subdomain can affect the entire domain's sending reputation. Monitoring each subdomain and ensuring it follows best practices is extremely important.
3 Jan 2022 - Word to the Wise
What the documentation says
4 technical articles
Email deliverability documentation consistently states that subdomain reputation significantly affects core domain reputation. Google's systems consider overall domain reputation, and poor subdomain reputation can negatively impact the main domain, though the main domain carries more weight. SparkPost highlights the influence of subdomain reputation on parent domain reputation, where good practices positively impact and poor practices negatively impact deliverability. Microsoft emphasizes that sender reputation calculations include both domain and subdomain, with issues on a subdomain affecting overall sender reputation and email sending ability. SendGrid explicitly states that the health of subdomains directly impacts the parent domain's health and recommends keeping subdomains in check.
Key findings
- Google's View: Google considers both subdomain and overall domain reputation, with some impact from subdomain to main domain.
- SparkPost's Influence: Subdomain practices, good or bad, directly influence parent domain deliverability.
- Microsoft's Calculation: Sender reputation considers both domain and subdomain; issues on a subdomain affect overall ability.
- SendGrid's Health Impact: The health of subdomains directly impacts the health of the parent domain.
Key considerations
- Monitor Subdomains: Regularly monitor subdomain health and sending practices.
- Implement Best Practices: Enforce good sending practices across all subdomains to positively influence the main domain.
- Maintain Subdomain Hygiene: Keep subdomains "in check" to prevent negative impact on the parent domain's reputation.
- Address Issues Promptly: Promptly address deliverability issues on subdomains to prevent broader reputational damage.
Technical article
Documentation from Microsoft shares that sender reputation is calculated on several things including the domain and subdomain the email is sent from. Issues from a subdomain will affect your overall sender reputation and ability to send email.
13 Apr 2025 - Microsoft
Technical article
Documentation from SparkPost explains that subdomain reputation influences parent domain reputation. Good sending practices on subdomains can positively impact the parent domain. Conversely, poor subdomain practices negatively impact parent domain deliverability.
1 Dec 2023 - SparkPost
Does Google Postmaster Tools domain reputation include subdomains?
Does subdomain data roll up to the root domain in Google Postmaster Tools?
How do subdomain deliverability issues affect parent domains, and what are the primary causes of email deliverability problems?
How do subdomain spam complaints affect root domain reputation in Google Postmaster Tools?
How does domain reputation affect subdomain reputation in email marketing?
How does parent domain reputation affect subdomain deliverability and sender reputation?
