Sender Reputation
Sender reputation is a score mailbox providers assign to your sending IP and domain based on past email behaviour, determining whether messages reach the inbox.
Sender reputation is the score that mailbox providers assign to your sending IP address and domain based on your historical email behaviour, which they use to decide whether your messages go to the inbox, spam, or nowhere at all.
What Sender Reputation Means in Marketing
You could write the best email campaign of your career and have it delivered to the spam folder of every recipient. Sender reputation is the invisible gatekeeper that decides whether that happens.
Mailbox providers like Gmail, Outlook and Yahoo track every signal associated with your sending address: how often recipients mark your emails as spam, how many of your messages bounce because the address doesn’t exist, whether recipients open and click or ignore everything you send, and whether your domain and IP have appeared on any blocklists.
These signals feed into a reputation score that is recalculated continuously. A good score means inbox placement. A poor score means spam. A very poor score means messages are silently discarded.
How Sender Reputation Works
Reputation exists at two levels. IP reputation is tied to the sending server’s address. Domain reputation is tied to your sending domain and its subdomains. Gmail and other major providers have shifted significant weight to domain reputation, which means switching to a new IP address won’t rescue a reputation problem if the domain is the issue.
The factors that build good reputation: sending to people who actually want your emails, maintaining a clean list (removing hard bounces promptly), keeping spam complaint rates below 0.1%, and sending consistently rather than in unpredictable spikes.
The factors that destroy it: buying email lists and sending to people who never opted in, ignoring bounce management, sending campaigns to a large list after months of silence, and using content patterns associated with spam.
Sender Reputation Example
A company acquires a list of business contacts through a trade show and blasts them all with a promotional email on a new dedicated IP address. The addresses include outdated contacts, spam traps left by mailbox providers to catch bad actors, and people who never agreed to receive marketing. Bounce rates hit 8%, several spam trap hits are registered, and the IP’s reputation is damaged within 48 hours. Future campaigns to their legitimate subscribers suffer because they now share that IP.
Why Sender Reputation Matters for Marketers
An email programme is only as valuable as the percentage of messages that actually reach the inbox. Reputation is what earns that access, and it is much easier to destroy than to rebuild.
Frequently Asked Questions
What damages sender reputation most?
High spam complaint rates are the biggest single factor. A spam complaint rate above 0.1% (one complaint per thousand emails) is considered problematic by most mailbox providers. Sending to invalid addresses that hard-bounce, sudden volume spikes, and low engagement rates over time also degrade reputation.
How long does it take to build sender reputation?
A new IP address or domain needs weeks of careful, gradually increasing sending to establish reputation. This is called IP warming. Starting by sending to your most engaged subscribers first, and slowly expanding volume and audience, signals to mailbox providers that you're a legitimate sender before you hit the full list.
Can sender reputation be repaired?
Yes, but it takes time. The fastest route is to stop sending to unengaged segments, clean the list of hard bounces and spam complaints, and rebuild with a smaller, more engaged audience. Some senders move to a new dedicated IP or subdomain and start fresh, with careful warming.