What does an ISP do?

ISP, or Internet Service Provider

An ISP, or Internet Service Provider, provides a mailbox to end users as part of their paid services. These are generally cable or internet providers like Comcast or Verizon.

An ISP is part of a larger category of inbox providers. These include ISP-provided inboxes, but also paid or free webmail accounts and email apps, such as Gmail, Outlook.com, Yahoo! Mail, or Inbox by Gmail.

ISPs, and inbox providers as a whole, play a huge part in determining design of the inbox, including what a subscriber sees as part of their envelope content (such as subject line, preview text, and from name.) They also affect deliverability for email marketers, since it’s part of their job to protect their users from bad or malicious senders. To accomplish this, they’ve created a series of filters, algorithms, spam traps, and other user tools such as “Mark as spam” buttons to attack spam.

They identify bad senders in a variety of ways:

What this means for email marketers is that as inbox providers succeed in blocking malicious spam, consumers’ definitions of what spam means to them has changed. As we argue in our report Adapting to Consumers’ Definition of Spam, consumers now unsubscribe and mark a brand’s emails as spam for the same reason.


ISPs are often confused with ESPs, or email service providers. ESPs provide platforms to send commercial or transactional email on your behalf. Common ESPs include Pardot, Emma, or MailChimp, but there are many to choose from.

The key difference is audience. An ESP is a tool used by marketers, while anyone with an email address is using an inbox provider.

Additional Resources

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