What is a shared IP?

Volume is what makes reputation legible. A pool sending millions of messages daily gives receivers a strong, continuous signal, and that steadiness is worth more than exclusivity to a small sender.

The platform's enforcement is what you are really buying. Providers that vet senders and evict bad ones keep pools clean; cheap ones with open signup do not, and you inherit whatever arrives.

The tradeoff is control. A neighbor's bad campaign moves your delivery, and there is nothing you can do about it except escalate and wait.

Your domain reputation stays yours throughout, and at Gmail it carries more weight than the connecting address does. That limits the damage a shared pool can do to a sender who behaves well.

Send yourself a campaign at a Gmail address and open Show original. Near the top you'll see a line like spf=pass (google.com: domain of bounces@em.acme.example designates 198.51.100.24 as permitted sender). That's the IP your platform used for this message.

Look up its reverse DNS with dig -x 198.51.100.24. A pooled address usually resolves to a generic name in the platform's own domain, something like o24.mail.sendplatform.example. Dedicated ones are often named after the customer. Then run the IP through a public blocklist checker.

Repeat the exercise over a few sends. Say you see five different addresses across five campaigns. That tells you you're on a rotating pool, and that one listed address out of five would affect roughly a fifth of your mail. It also gives you something specific to bring to support: an IP, a date, and the name of the list it appeared on.

Ask how pools are tiered. Most large platforms don't put every customer on the same addresses. New accounts, free plans and senders with poor metrics often share one set of IPs, while established senders with clean numbers share another. You want to know which tier you're in and what moves you up.

Ask what gets a customer removed, in numbers. A provider that can say we suspend at a 0.5% complaint rate or a 5% bounce rate is policing its pool. One that answers with general reassurance probably isn't.

Ask whether transactional and marketing traffic use separate pools, because your password resets shouldn't ride with anyone's promotions, including your own.

Your own list quality still feeds into this. On a policed pool, the sender who gets suspended for a bounce spike could be you. A file you've verified before importing is the simplest way to stay on the right side of whatever thresholds your provider enforces.