What are the implications of sharing a subdomain between two different ESPs?

Sharing a subdomain across multiple ESPs presents significant challenges to email deliverability. Central concerns include managing sender reputation, handling DNS conflicts, and navigating the complexities of email authentication protocols. Using a shared subdomain can lead to reputation dilution, where one ESP's poor sending practices negatively affect the others. Managing SPF records, DKIM keys, and DMARC policies also becomes more complicated, increasing the risk of authentication failures. While it may be technically possible under certain conditions, such as if the primary ESP controls DNS and allows changes, it is generally advised to use dedicated subdomains for each ESP. This allows for better isolation of deliverability issues and provides more control over sender reputation.

Sharing a subdomain between multiple ESPs can lead to several deliverability complications. Managing DNS records, especially SPF records, becomes more complex, increasing the risk of authentication failures. Sender reputation is also a significant concern, as one ESP's poor sending practices can negatively impact the entire subdomain's reputation, affecting deliverability for all users. While some experts acknowledge that sharing subdomains is possible under specific conditions (e.g., the current ESP controls DNS and allows changes), it is generally not recommended. Using dedicated subdomains for each ESP is preferred, as it allows for better isolation, management, and control of sender reputation and helps to identify and resolve issues more effectively.

Sharing subdomains across multiple ESPs is generally discouraged due to the negative impact on sender reputation. Each ESP's sending practices influence the overall subdomain reputation, making it difficult to isolate and address deliverability issues. Avoiding the use of the same sending address and subdomain across multiple platforms is recommended to prevent one platform's reputation from negatively affecting the other. Employing dedicated subdomains allows for better management and control, enhancing deliverability.

Sharing a subdomain between multiple ESPs introduces complexities related to DNS management, authentication, and policy enforcement. While subdomain delegation can provide each ESP with full DNS control through separate zones, the DMARC and DKIM standards highlight the challenges in maintaining alignment and managing multiple keys. Maintaining up-to-date SPF records, especially when multiple senders are involved, is critical to avoid authentication failures. These complexities can lead to deliverability issues if not carefully managed.