Infrastructure
What is Mailbox Provider (MBP)?
The company that operates the receiving email infrastructure and inboxes for recipients, such as Google, Microsoft, or Yahoo.
A mailbox provider, sometimes called a receiver, runs the servers, spam filters, and inbox UI that accept and sort mail for end users, distinct from an ESP that helps senders send. Major consumer providers include Gmail, Microsoft Outlook and Hotmail, and Yahoo, while businesses commonly use Google Workspace or Microsoft 365. Each applies its own authentication requirements, reputation systems, and filtering rules, so deliverability outcomes differ by provider.
Why it matters for cold email
Inbox placement is decided by the recipient's mailbox provider, so a cold campaign can inbox at one provider and hit spam at another based on that provider's rules and your reputation with it. Knowing which providers dominate a list lets you tune authentication, warmup, and volume to each, and use their postmaster tools to monitor standing.
Related terms
Stop guessing at deliverability.
Scheduler Zero handles authentication, warmup, and sender reputation so your cold email lands in the inbox, not the spam folder.