What is IP reputation?

IP reputation is what inbox providers think of the mail server your emails come from. Every time you send an email, it leaves from a specific IP address. Inbox providers track what that IP does. Lots of spam from that IP? Bad reputation. Clean sending history, low complaints, good engagement? Good reputation.

IP reputation is based on behavior over time. Inbox providers (like Gmail, Outlook, and Yahoo) watch for spam complaints, bounce rates, spam trap hits, and engagement patterns. If an IP sends mail that people mark as spam, or if it hits addresses that don't exist, that IP's reputation drops. If it sends mail people open and engage with, reputation goes up.

There are two types of IP setups: shared and dedicated. Most senders start on a shared IP. That means you're sharing the same mail server with dozens or hundreds of other senders. If one of them screws up (buys a list, sends spam, triggers complaints), everyone on that shared IP feels it. The upside is that if you're new and sending low volume, you benefit from the good behavior of everyone else. ESPs like Mailchimp and Brevo put most users on shared IPs because it's easier to manage reputation at scale.

A dedicated IP means you're the only sender using that address. You control the reputation completely. No one else's mistakes hurt you. But that also means you start with zero reputation, and you have to build it from scratch. That takes time and consistent sending. If you send 50,000 emails one month and nothing the next, inbox providers don't trust the pattern. Dedicated IPs make sense if you send high volume consistently (think 100k+ emails per month) and have clean list practices.

IP reputation is only one part of sender reputation. Inbox providers also look at domain reputation (the from-domain in your emails) and content signals. But IP reputation still matters, especially for transactional senders on dedicated IPs or anyone dealing with a sudden reputation drop.

If you're on a shared IP and your deliverability tanks, check if your ESP will tell you why. Some won't, but it's worth asking. If you're on a dedicated IP, you can check your reputation yourself with our free blocklist checker. (Blocklists are one fast way to see if your IP has a problem, though they're not the whole picture.) If your IP shows up on major blocklists, that's a red flag worth fixing.