Do ESP IP pools always share risk equally?

You signed up with a reputable ESP, you're sending clean campaigns, your list is opted in, and your open rates are solid. Then one day your delivery dips for no obvious reason. Sound familiar? The culprit might not be you at all. It might be someone else on your shared IP pool.

Shared IP pools do not spread risk equally. The idea that everyone shares the same fate proportionally is a myth worth unpacking. Your reputation contributes to pool health based on your volume and behavior, but so does every other sender on that pool. A high-volume spammer dropped into your pool does a lot more damage than a small legitimate sender can offset.

Here's how it actually works. Your ESP routes outgoing email through a group of shared IP addresses. Mailbox providers like Gmail and Outlook build reputation signals against those IPs. If another sender on your pool triggers spam complaints, mailbox providers start viewing every IP in that pool with more suspicion. You didn't send a single bad email, but your delivery rate drops anyway. It's frustrating, and it's common.

The reverse is also true. Good senders help pool health, but the benefit is not symmetric. Reputation damage from one bad actor spreads faster than the goodwill built up by a dozen clean senders. (That asymmetry is just the reality of how spam filtering works.)

How to tell if your pool is struggling

Watch for these signals:

• Sudden dip in open rates without any change to your own sending behavior or list quality
• Increased soft bounces, especially with vague codes like "Service temporarily unavailable" or "Connection refused"
• Gmail Postmaster Tools showing IP reputation dropping while your domain reputation stays stable (that gap tells you the problem is the IP, not your domain)
• Blocklist hits on your sending IPs that you didn't cause

And you can check your sending IPs against major blocklists using our free blocklist checker. If your IPs are listed and you've been sending clean campaigns, it's a pool problem, not a you problem.

What to do about it

First, find out how your ESP manages pool hygiene. Good ESPs actively remove bad senders, segment pools by sender quality, and respond quickly when pool IPs get listed. If your ESP can't tell you how they handle this, that's a red flag.

Second, look at your own position within the pool. If you're a mid-to-high volume sender (say, above 100,000 emails per month), you're likely in a more curated segment than a new account sending 5,000 emails. Volume matters for how ESPs assign senders to pools, and higher-quality pools tend to have fewer bad actors because the volume requirements act as a natural filter.

Third, consider whether you've outgrown shared IPs. A dedicated IP means your reputation is entirely your own. No one else can drag it down. But it also means you own it completely, including warming it, maintaining it, and recovering it if something goes wrong. It's not automatically better, it's just yours.

And if pool issues are actively hurting your delivery right now and you're not sure what to do next, our SOS hotline is free. Sometimes it just helps to talk through the situation with someone who isn't trying to sell you a platform upgrade.