How much does subdomain reputation affect core domain reputation?

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.

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.

Email marketer from StackExchange mentions that subdomains provide a degree of separation but are still linked to the main domain. A compromised subdomain will eventually degrade the entire domain's reputation.

Marketer from Email Geeks states that it's always better to use individual domains (or even dedicated ones) with unique email authentication and list management for senders.

Email marketer from EmailOversight explains that poor sending practices can negatively impact not only the subdomain's reputation, but also the reputation of the main sending domain. Deliverability may suffer across the board.

Email marketer from Litmus mentions that subdomains are useful for segmenting sending practices. However, a poor subdomain will cause issues for the whole domain reputation.

Email marketer from Mailjet Support shares that while subdomains allow for segmentation, issues with a subdomain can impact the overall domain reputation. They recommend carefully monitoring subdomain performance to prevent damage to the core domain.

Marketer from Email Geeks suggests signing separately on behalf of each publisher using DKIM with a different domain or selector for each publisher.

Email marketer from Email Marketing Forum shares that subdomains can help segment reputation, but a spammy subdomain can still damage the main domain's deliverability. They suggest only using subdomains for legitimate, high-quality email.

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.

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.

Expert from Spam Resource explains that a subdomain's reputation directly impacts the parent domain's deliverability. Poor sending practices on a subdomain will negatively affect the overall domain's ability to reach the inbox. It's crucial to maintain good sending habits across all subdomains.

Expert from Email Geeks shares that for individual clients, it's always better to use their own domains for authentication and click links, noting that complete isolation (outside of dedicated IPs with custom rDNS) is nearly impossible.

Expert from Email Geeks notes that blocklists often list the parent domain, regardless of subdomain reputations. If you’re trying to avoid blocklisting, then you should use different domains.

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.

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.

Documentation from SendGrid states that the health of your subdomains will directly impact the health of your parent domain. They recommend keeping your subdomains in check.

Documentation from Google explains that while subdomains have their own reputation, Google's systems consider the overall domain reputation. A poor subdomain reputation can negatively impact the reputation of the main domain, and vice versa, though the main domain typically has more weight.