Sender Reputation
Email MarketingAlso: Email Sender Reputation · IP Reputation · Domain Reputation
Quick definition
Sender reputation is the trust score mailbox providers like Gmail and Outlook assign to your sending infrastructure. It determines whether your emails reach the inbox, land in spam, or get blocked entirely. It is built on your IP address history, your sending domain, and how recipients have responded to your emails over time.
How it varies across Australia
Sender reputation problems are more common than most Australian email senders realise. Deliverability issues often look like engagement problems until someone checks the headers. Lists grown through high-volume acquisition funnels tend to carry the heaviest reputation debt.
See email marketing performance across Australian industries →The main signals mailbox providers use
The share of recipients who mark your email as spam. The single most damaging signal.
Danger zone: above 0.1%Emails that couldn't be delivered because the address doesn't exist or the inbox is full.
Hard bounces should be removed immediatelyOpens, clicks and replies signal to mailbox providers that recipients want your emails.
Positive signal, weighted heavily by GmailTechnical records that prove you are who you say you are. Required for inbox delivery.
All three should be configured and passingWhat it actually means
Sender reputation is the invisible door that decides whether your email ever reaches the person you sent it to. Mailbox providers like Gmail, Outlook and Apple Mail each run their own scoring systems. Every time you send an email, they update their picture of you based on what recipients do with it.
There are two layers to sender reputation. The first is IP reputation: the score attached to the specific IP address your emails go out from. If that IP was used previously by a spam operation, or if your volume spikes unpredictably, the IP score takes the hit. The second layer is domain reputation: the score attached to your sending domain. Google in particular has shifted heavily toward domain reputation as the primary signal, which means a damaged domain is a serious problem that IP warming alone won't fix.
The signals mailbox providers watch include spam complaint rates (how often recipients hit 'report spam'), bounce rates (how many addresses don't exist), unsubscribe rates, engagement rates (opens, clicks, replies), and whether your authentication records are correctly set up.
The thing that catches most senders off guard: reputation damage is slow to accumulate and slow to recover. You can't send your way out of a bad reputation quickly. The repair work is methodical, not fast.
You can write the best email in the world. If your sender reputation is broken, no one reads it.
How it shows up
Sender reputation shows up most clearly in deliverability data. Gmail Postmaster Tools shows domain reputation and spam rate as a direct read from Google's infrastructure. The categories are high, medium, low and bad. Landing in 'low' is a warning. 'Bad' means a material share of your emails are going to spam for Gmail recipients.
Microsoft SNDS provides a similar signal for Outlook and Hotmail addresses. If you're not monitoring either of these, you're guessing.
Less directly, it shows up as falling open rates, rising unsubscribe rates, and a growing gap between what your email platform reports as delivered and what recipients actually see. When your platform says 98% delivered but engagement has halved, reputation is usually the culprit.
The Australian context
Australian email marketers operate under ACMA's Spam Act 2003, which requires explicit consent for commercial emails and a functioning unsubscribe mechanism. Non-compliance produces complaint rates that directly damage sender reputation.
Australian consumer email is dominated by Gmail and Outlook just as it is globally, so the same reputation signals apply. However, several Australian ISPs and telcos (Bigpond, TPG, Optus-hosted mail) run their own filtering systems with less transparent documentation. Senders targeting older demographic segments who still use ISP-provided email addresses often encounter harder-to-diagnose deliverability issues from these systems.
One Australia-specific wrinkle: businesses using shared IP pools through popular local email-service-providers sometimes inherit reputation problems from other senders on the same pool. If your deliverability deteriorated with no obvious cause, ask your provider whether your IPs are shared and what reputation monitoring they run.
Where people get this wrong
Related terms
Common questions
How do I check my sender reputation?
Start with Gmail Postmaster Tools for Google's direct read on your domain reputation and spam rates. For Outlook, use Microsoft's SNDS (Smart Network Data Services). Third-party tools like MXToolbox and GlockApps provide broader inbox placement testing across multiple providers. Set these up before you need them.
How long does it take to repair a damaged sender reputation?
Weeks to months, not days. Recovery requires stopping the damaging behaviour, shrinking your active list to highly engaged recipients, sending at reduced volume, and rebuilding slowly while monitoring postmaster data. There is no shortcut. Anyone selling a quick-fix is selling something else.
Does switching email platforms fix reputation problems?
Switching platforms changes your IP addresses, which can give you a temporary clean slate on IP reputation. It does not fix domain reputation, which follows your sending domain. If domain reputation is damaged, switching platforms buys you time, not a solution.
What spam complaint rate is considered safe?
Google's own guidance recommends keeping spam complaint rates below 0.10% and strongly advises staying below 0.30%. Above 0.10% you will start seeing deliverability effects for Gmail recipients. The threshold for other providers varies but the same principle applies: one complaint in every thousand sends is already a signal to take seriously.
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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.
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