The consensus across experts, marketers, and documentation sources is that a parent domain's reputation significantly impacts the deliverability and sender reputation of its subdomains. While subdomains are often used to isolate email streams and protect the main domain, they are not entirely independent. A poor parent domain reputation, resulting from spam complaints, blacklisting, or other negative sending practices, can negatively impact subdomain deliverability. Google's machine learning algorithms recognize attempts to use subdomains to circumvent filters when the parent domain has a bad reputation, treating new subdomains with suspicion. Consequently, fixing the parent domain's reputation becomes crucial. Furthermore, ISPs and search engines consider the association between parent domains and subdomains when filtering emails. Maintaining proper email authentication, good list hygiene, and regularly monitoring the reputation of both the parent domain and subdomains are vital for ensuring successful email deliverability.

The reputation of a parent domain significantly influences the deliverability and sender reputation of its subdomains. While subdomains can help isolate email streams and protect the main domain, they are not entirely independent. A poor parent domain reputation, stemming from spam complaints, blacklisting, or other negative sending practices, can negatively impact subdomain deliverability. Setting up infrastructure correctly, implementing authentication, and maintaining good list hygiene are also essential. Despite the benefits of subdomains, awareness of the parent domain's reputation is crucial for achieving good deliverability.

The parent domain's reputation significantly impacts subdomain deliverability. A bad parent domain reputation affects the subdomain's reputation, especially with Gmail, as Google's machine learning detects attempts to evade filters. Although subdomains can isolate reputation, a badly damaged parent domain can still negatively impact them, causing deliverability issues. If test messages go to spam, building a reputation becomes difficult, emphasizing the need to fix the parent domain's reputation and rehabilitate it to allow Gmail recipients who override spam filters to receive emails. Monitoring both the subdomain and parent domain reputation is crucial, as ISPs can consider the overall domain family when filtering, particularly if there's evidence of coordinated spam activity across multiple subdomains. Removing inactive recipients from the list is also advisable.

According to documentation from Google Workspace, SendGrid, Microsoft Learn and SparkPost, parent domain reputation significantly impacts subdomain deliverability. Google considers the parent domain's reputation when evaluating subdomains, and a negative reputation can negatively impact email deliverability. Similarly, SendGrid indicates that while subdomains allow segmentation and improved reputation management, a severely damaged parent domain can still hinder the subdomain's performance. Microsoft Learn emphasizes that poor sending practices from the parent domain can negatively affect subdomains, leading to spam filtering. SparkPost reinforces that parent domain reputation affects subdomain deliverability, posing challenges despite the segmentation benefits of subdomains.