What’s the difference between senders, ESPs, and MBPs?
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When your email lands in someone's inbox (or doesn't), three different parties were involved in that outcome. Understanding who does what makes it a lot easier to figure out who to call when something goes wrong.
You're the sender. You decide what to send, who receives it, and when. That also means you own the responsibility for having permission to email those people, keeping your list clean, and making sure the content is accurate and legal. No one else can take that off your plate.
An ESP (Email Service Provider) is the platform you use to send. Mailchimp, Klaviyo, Brevo, and Twilio SendGrid are ESPs. They give you the sending infrastructure, list management tools, templates, and analytics. They send on your behalf using their servers and IP addresses, which means their reputation is tied to yours (and yours to theirs). If you send spam through an ESP, they can and will shut your account down.
An MBP (Mailbox Provider) is where your recipient's email lives. Gmail, Outlook, Yahoo Mail, and Apple iCloud Mail are MBPs. They receive the email your ESP just sent and then decide what happens to it. Inbox, spam, or rejected outright. Their job is to protect their users, not to help you reach them.
The reason this distinction matters is accountability. Your ESP can't fix bad list hygiene on your end. An MBP won't tell your ESP why it rejected a message. And as the sender, you're the only one with full visibility into how the whole ecosystem connects. Knowing where the boundaries are helps you ask better questions and fix problems faster.
Want to see how an email actually moves through all three layers? Check out how an email travels through the ecosystem.
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