IP Reputation
Email MarketingAlso: Sender IP Reputation · Sending Reputation
Quick definition
IP reputation is the trust score mailbox providers like Gmail and Outlook assign to the server address your emails send from. A good reputation gets your email into the inbox. A poor one gets it filtered to spam or blocked outright, regardless of how good the content is.
How it varies across Australia
Most Australian businesses sending through shared IPs on mainstream email service providers never think about IP reputation because the provider manages it for them. The businesses that run into trouble are almost always the ones who moved to a dedicated IP too early, without enough volume to build reputation, or who bought a list.
See email deliverability benchmarks across Australian industries →What it actually means
Think of IP reputation like a credit score, except the lender is Gmail and the currency is trust. Every time you send email, mailbox providers watch how recipients react. Do they open it? Delete it unread? Mark it as spam? Does the email bounce because the address doesn't exist? All of that gets logged against the sending IP address, and the running total decides whether your next email lands in the inbox, the spam folder, or nowhere at all.
This sits next to but separate from domain reputation and authentication protocols like SPF, DKIM and DMARC. Authentication proves you are who you say you are. Reputation is the judgement call about whether that's a good thing. You can pass every authentication check and still get filtered to spam because your IP has a poor sending history.
Most small and mid-sized senders use a shared IP through their email service provider (ESP), which pools reputation across many senders. That protects you from small mistakes but also means someone else's bad behaviour can drag your deliverability down. Dedicated IPs put the reputation entirely in your hands, for better or worse.
Your subject line doesn't matter if the mailbox provider already decided not to trust the address it came from.
How it shows up
IP reputation shows up as a slow, unexplained decline in open rate that no content change fixes. It shows up when Gmail Postmaster Tools flags your domain reputation as anything below high. It shows up as bounces that used to be soft suddenly turning hard, or as entire sends landing in the promotions or spam tab overnight after a list import. The tell-tale sign is a deliverability problem that correlates with a sending change, not a content change: a new IP, a purchased list, a sudden volume spike, or a migration to a new email service provider.
The Australian context
Australian senders using overseas ESPs sometimes inherit reputation issues from IPs previously used by unrelated senders in other markets. Because Australia is a small market for most global ESPs, dedicated IP warmup guidance is often written for US-scale volumes and doesn't translate cleanly to a business sending a few thousand emails a week. Slower, more conservative warmup schedules tend to serve Australian mid-market senders better than the defaults built into most platforms.
Where people get this wrong
Related terms
Common questions
How do I check my IP reputation?
Gmail Postmaster Tools is the most reliable free option if you send meaningful volume to Gmail addresses. Third-party tools like Sender Score and Google's own reputation dashboards also give a directional read. Most email service providers surface deliverability warnings internally too.
Should I use a shared or dedicated IP?
Shared IPs suit most small and mid-sized senders because the provider manages reputation and pools risk across many senders. Dedicated IPs make sense once you're sending consistently high volume and want full control, but only if you can maintain that volume to keep the IP warm.
Can a damaged IP reputation be fixed?
Yes, but it takes time, not a quick switch. Stop sending to unengaged contacts, clean your list, fix authentication, and send consistent, wanted content for several weeks. Mailbox providers rebuild trust gradually, they don't reset it instantly.
Does IP reputation matter if I use a big ESP like Klaviyo or Mailchimp?
It still matters, but the ESP absorbs most of the risk on shared IPs by monitoring senders and removing bad actors from the pool. Your own sending behaviour, list quality and complaint rates still contribute to how that shared pool performs.
Debrief
Get the next one
No spam. No fluff. Just the next article, straight to your inbox.
Keep exploring
About New Rebellion
New Rebellion is a marketing intelligence consultancy. We build tools, score Australian businesses on how their marketing actually performs, and publish Debrief every day. This dictionary is part of how we work in the open.
How we think →