IP Reputation

Before a receiving server even reads your message, it can look up the IP address the connection is coming from and ask a simple question: what kind of mail has this address sent lately? The answer is its IP reputation, a running score built from complaint rates, spam-trap hits, bounce volume, sending patterns, and whether the IP appears on any blacklist.

Reputation is bound to the address itself, not to you. That has two consequences. First, a freshly provisioned IP has no history and is treated with suspicion until it earns trust through warmup. Second, if you later move to a different IP, you leave the old reputation behind, good or bad, and start building again.

No mailbox provider hands you its internal per-IP number. What you can see instead are the public signals that drive it: whether the IP appears on a major blacklist, how clean its sending history looks, and how receivers respond to it. Providers weigh recent behaviour most, typically over a rolling 30-day window, so a single bad day fades but a sustained problem compounds.

That public number is only a proxy. Each mailbox provider also keeps its own private per-IP view, and blacklist operators publish their own verdicts. You cannot see Gmail’s internal IP score directly, but you can watch the signals that drive it: your blacklist status, your complaint rate, and your throttling responses.

Whether the reputation is yours alone depends on the IP model. On a dedicated IP, every message comes from you, so the reputation is entirely your own to build and to ruin. On a shared IP, you send alongside other customers of the same ESP, and the IP’s reputation is the blend of everyone’s behaviour. A good neighbour’s steady volume can lend a small sender instant credibility; a bad neighbour can tank delivery you had nothing to do with.

Dedicated IPs reward high, consistent volume (enough mail to maintain a clear signal) and demand a full warmup. Shared IPs suit lower or spiky volume because the pool’s aggregate traffic keeps the reputation warm, at the cost of control. Either way, the domain in your From: carries its own domain reputation on top, which increasingly matters more than the IP.

• Warm a new IP. Never blast from a cold address. Ramp volume gradually so providers see a believable growth curve.
• Watch blacklists. A listing on Spamhaus or a similar DNSBL can block mail outright. Monitor with our Blacklist Checker and act on listings fast.
• Set correct reverse DNS. A matching PTR record and forward-confirmed reverse DNS are baseline expectations; a mismatch quietly suppresses delivery.
• Keep volume steady. Sudden spikes from a previously quiet IP look like a compromised server and invite throttling.
• Protect the complaint rate. The fastest way to wreck any IP’s reputation is a flood of spam complaints from a poorly targeted send.