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Email Marketing Glossary.

Clear, no-fluff definitions of every email marketing term that matters—from open rates to double opt-in. 

 

Mailbox Provider

A mailbox provider (sometimes called an ISP) is a service that hosts and delivers email inboxes—like Gmail, Yahoo, and Outlook—and decides whether your email lands in the inbox or spam.

Also known as: ISP, inbox provider, email provider

Behind every subscriber is a mailbox provider deciding what reaches them. Gmail, Yahoo, Outlook, and Apple Mail are the gatekeepers whose rules shape everything about deliverability.

Mailbox provider vs. ISP

Historically these were the same—your internet service provider gave you email—but today major inboxes are run by mailbox providers like Google and Microsoft. The terms are often used interchangeably.

Why do mailbox providers matter?

They enforce authentication requirements, evaluate your sender reputation, and decide inbox versus spam placement. Meeting their standards—like Gmail and Yahoo's sender requirements—is essential.

How do you stay in their good graces?

Authenticate your domain, keep complaints under 0.3%, mail engaged subscribers, and honor unsubscribes. Each major provider offers tools like Google Postmaster Tools to monitor your standing.

Related terms

Sender Score IP Warming Dedicated IP Feedback Loop Email Authentication Blocklist BIMI Sender Reputation SPF DKIM DMARC Hard Bounce Soft Bounce Spam Trap Inbox Placement Sending Domain Email Deliverability

Related reading from Drip

Ecommerce Email Deliverability: 9 Ways to Reach the Inbox What's a Good Email Deliverability Rate in 2026?

Frequently asked questions

What is a mailbox provider?
A mailbox provider is a service that hosts and delivers email inboxes—such as Gmail, Yahoo, Outlook, and Apple Mail. It decides whether your emails reach the inbox, the spam folder, or a tab like Promotions.
What's the difference between a mailbox provider and an ISP?
Historically your internet service provider (ISP) also provided email, so the terms overlapped. Today major inboxes are run by dedicated mailbox providers like Google and Microsoft, though 'ISP' is still used loosely to mean the same thing.
Why do mailbox providers matter for email marketing?
They enforce authentication requirements, judge your sender reputation, and decide inbox versus spam placement. Meeting their standards, such as Gmail and Yahoo's sender requirements, is essential to reaching subscribers.
How do I stay in good standing with mailbox providers?
Authenticate your domain with SPF, DKIM, and DMARC; keep spam complaints under 0.3%; mail only engaged subscribers; and honor unsubscribes promptly. Tools like Google Postmaster Tools help you monitor your reputation.
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