DMARC.quest
You need this. You don't even need to sign in. Just go to the site and enter a domain name you have outbound email from. When you setup DMARC you need an address to receive reports -- DMARC.quest can do intake, but unlike others an AI agent monitors them intelligently over time, alerting you to real signal over noise. Yes the UI is still a sloppified mess, but the quality of analysis of the agent is world class, this discovers configuration issues all the time, even in very technically sophisticated companies.