How do MBPs differ from ESPs?

MBPs and ESPs serve fundamentally different roles in the email ecosystem. A mailbox provider (MBP) like Gmail or Outlook hosts recipient inboxes and decides whether your email lands in the inbox, spam, or gets rejected entirely. An email service provider (ESP) like Mailchimp or Klaviyo helps you send emails at scale.

Think of it this way: your ESP is your shipping company that packages and dispatches your mail. The MBP is the postal service at the destination that inspects packages and decides which ones get delivered to the mailbox versus flagged as suspicious.

ESPs handle list management, template design, sending infrastructure, and analytics. MBPs handle receiving, filtering, spam detection, and inbox organization. Your deliverability depends on how well your ESP's practices align with what MBPs expect from legitimate senders.