Mailbox provider

Mailbox providers (also called "receivers" or "MBPs") are who decide whether your email lands in the inbox, the promotions tab, the spam folder, or gets bounced. Each one has its own reputation system, content filters, and engagement signals.

Reputation is per-provider — Gmail might love you while Outlook hates you. BoomSauce reports reputation segmented by provider (Gmail / Google Apps / Outlook / Yahoo / Other) because the diagnosis path differs for each.