The Return Path Seed List is a collection of email addresses owned by Return Path where you send your email campaigns for testing in order to collect important deliverability data. Each email address is called either a CoreSeed or a SmartSeed. CoreSeeds track how your email is being placed by mailbox providers, while SmartSeeds provide visibility into subscriber engagement.
The Return Path Seed List is composed of CoreSeed addresses at mailbox providers and business-to-business (B2B) filters and email hosting providers throughout Australia, Europe, Latin America, and North America, including AOL, Gmail, Yahoo!, and others, as well as SmartSeed addresses at Gmail, Microsoft, and Yahoo!.
However, it's important to note that Return Path does not have any partnerships or agreements with mailbox providers that influence seed inbox placement data. Deliverability results are reflective of a sender's reputation and overall email campaign performance.