All major consumer and business email providers: Gmail, Outlook/Hotmail/Office365, Yahoo/AOL, Apple iCloud, Proton Mail, Zoho, and many ISPs. Enterprise mail gateways (Barracuda, Mimecast, Proofpoint) also send reports when handling inbound email. The more mail your domain receives, the more report sources you’ll see. Small domains may only get reports from Gmail and Outlook.
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