Does Google Postmaster Tools domain reputation include subdomains?

There's no definitive consensus on whether Google Postmaster Tools (GPT) includes subdomains in the root domain's reputation calculation. Some data suggests Google explicitly tells users subdomains are not included, yet inconsistencies are seen in GPT data. Experts and marketers recommend using subdomains to isolate reputation and separate different email types (transactional vs. marketing). However, the root domain remains essential for reputation checks. Google's documentation requires authentication for data visibility but is vague on aggregation. RFC standards define subdomains as separate, and it is very important to warm them up before starting a campaign.

Experts and marketers offer conflicting views on whether Google Postmaster Tools (GPT) domain reputation includes subdomains. Some sources report explicit statements from Google indicating subdomains are not included in the organizational domain's reputation. However, others express doubt, noting that GPT sometimes displays a reputation even when the organizational domain itself doesn't send mail. Further, differing GPT reputations are observed for parent domains and subdomains. The use of subdomains is generally recommended for isolating reputation and separating different types of email traffic (e.g., transactional vs. marketing), but root domains are still the core part of where reputation is checked.

Experts offer insights into how Google Postmaster Tools (GPT) handles domain and subdomain reputation. One expert assumes root domain reputation includes subdomains. While focusing on the d= for reputation, there's a suggestion Google might include subdomains in root calculations, separating it out with the FBL identifier. Other experts emphasize using subdomains to protect the primary domain's reputation by isolating different types of email traffic and their reputation.

Google's documentation states that Postmaster Tools data is aggregated for domains passing authentication (SPF, DKIM, DMARC), and authentication is required to view the data. However, it doesn't clarify if subdomains are aggregated into the root domain's reputation or kept separate. Other documentation sources (RFC, Microsoft, Cloudflare) confirm that subdomains are distinct domains, treated differently from the top-level domain, and that domain names form the base of email and web addresses.