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.