What Is Sender Reputation? How It's Scored
Also known as Email sender reputation, Sender score
Sender reputation is the trust level that mailbox providers such as Gmail and Outlook assign to a sender, based on the history of its sending domain and IP address. It is shaped by spam complaints, bounces, spam trap hits, authentication results and engagement. A strong reputation helps emails reach the inbox, while a weak one pushes them to spam.
Sender Reputation explained
Every major mailbox provider keeps its own internal view of each sender. There is no single public score. Providers track signals like how often recipients mark your mail as spam, how many addresses bounce, whether you hit spam traps, whether SPF, DKIM and DMARC pass, and how people engage: replies, reads, deletes and moving mail out of spam. Each provider weighs these differently and does not publish the formula.
Reputation is attached mainly to two things: your domain and the IP addresses you send from. When you use Google Workspace or Microsoft 365, the IPs are shared and managed by the provider, so for most cold email teams domain reputation matters most. Dedicated IPs through an email service provider put more of the IP history on you.
For outbound, reputation is built slowly and lost quickly. Warm-up, sensible daily volume, verified lists and relevant targeting build it. A single bad list upload or a spike in complaints can undo weeks of work. That asymmetry is why experienced teams separate outbound onto secondary domains and watch metrics every week.
Sender Reputation example
A team uploads an old trade show list of 2,000 contacts and sends it all in two days. 9% bounce, several addresses are recycled spam traps and complaints rise. Within a week, emails from that domain land in spam at Gmail. Replies on their other campaigns from the same domain fall too, because reputation is tied to the domain, not the campaign.
How to improve sender reputation
Check where you stand
Review Google Postmaster Tools for your domain, Microsoft SNDS if you have dedicated IPs, blacklist checkers, and your own bounce and complaint numbers.
Stop the damage first
Pause sending from affected mailboxes, remove the list segment that caused trouble and fix any failing SPF, DKIM or DMARC checks.
Clean and verify lists
Verify every address before sending and remove invalid, risky and long-inactive contacts to cut bounces and spam trap hits.
Rebuild with low volume
Restart with small daily volumes to your most relevant contacts, keep warm-up running, and ramp slowly as complaints and bounces stay low.
Earn real engagement
Send fewer, more targeted emails that people reply to. Replies and positive interactions are some of the strongest positive signals you can generate.
Common mistakes
- Assuming one third-party score reflects how Gmail or Outlook actually see you.
- Blasting purchased or old lists, which brings bounces, spam traps and complaints together.
- Running all outbound from the primary domain, so cold email problems hit transactional and team email.
- Raising volume as soon as results look good instead of ramping gradually.
Sender Reputation FAQ
Use Google Postmaster Tools for Gmail data on your domain, Microsoft SNDS for your IPs if you have dedicated ones, and blacklist lookups. Third-party scores like Sender Score give a rough view of IP reputation. Your own bounce, complaint and reply trends are often the most practical signal.
Mailbox providers do not publish scores. Third-party tools use their own scales, so a good number on one tool is not comparable to another. Treat any score as a rough guide and focus on the inputs: low complaints, low bounces, passing authentication and steady engagement.
Not instantly. You can recover it by fixing the cause, cutting volume, cleaning lists and sending only to engaged, relevant contacts over several weeks. For a heavily damaged secondary domain used for cold email, many teams retire it and start fresh on a new warmed domain.
Both. Providers track the reputation of your sending domain and the IPs you send from. On Google Workspace or Microsoft 365 the IPs are shared and managed, so your domain reputation does most of the work. On dedicated IPs, IP history matters much more.