Several major ISPs offer domain-based Feedback Loops (FBLs) that utilize DKIM for senders who properly authenticate their mail. The key ISPs that offer FBLs based on DKIM are Gmail, Yahoo, and AOL. While iCloud does not offer a FBL, senders can use Validity's Universal Feedback Loop, which consolidates data from multiple ISPs. Microsoft utilizes IP-based FBL, but provides SNDS to monitor IP reputation, which indirectly impacts domain performance. DKIM is fundamental for establishing these feedback loops and is required by most major ISPs to provide feedback loops, allowing senders to understand if their users are marking the email as spam. Whitelisting, which involves listing your email or IP address as a safe sender, can assist with deliverability in corporate environments. Resources like ReturnPath offer tools to use DKIM-based feedback loops to gain complaint data directly from ISPs. Monitoring tools, such as Spam Resource, also offer insights into senders' reputations, domains, and ISPs.