Sender reputation is the score mailbox providers (Gmail, Yahoo, Outlook, Apple) silently keep on every domain and IP that sends email. Above a certain threshold, your messages go to the inbox. Below it, they go to spam, or get rejected entirely. It is the single most important variable in deliverability, and most senders never check theirs.
What goes into sender reputation
Every mailbox provider runs its own scoring system, but the inputs are roughly the same everywhere:
- Bounce rate. The percentage of emails that fail to deliver. Above 2% is a red flag.
- Complaint rate. How often recipients mark your mail as spam. Above 0.1% is bad.
- Engagement rate. Opens, clicks, replies. Higher is better.
- Authentication. SPF, DKIM, DMARC. Pass all three.
- Volume consistency. Sending 100 emails on Monday and 100,000 on Tuesday looks suspicious.
- Spam trap hits. Hitting a single spam trap can torpedo your reputation for weeks.
- List hygiene. Repeated sends to invalid addresses signal a stale or purchased list.
Domain reputation vs IP reputation
Two reputations exist in parallel. Your sending domain (the part after the @ in your From line) carries one. The IP address you send from carries another. If you use a shared sending service like Mailchimp or SendGrid, the IP is shared with thousands of other senders; the domain is uniquely yours.
This matters because if you switch ESPs, your IP reputation resets but your domain reputation follows you. A clean domain reputation means you can recover from an ESP migration in a week. A trashed one means a fresh start.
How to check your sender reputation
Google Postmaster Tools
Free, run by Google. Verify your domain and you can see Gmail's view of your IP reputation, domain reputation, spam complaint rate, authentication pass rate, and delivery errors. It is the closest thing to ground truth most senders will see.
Microsoft SNDS
Same idea, for Outlook/Hotmail. Less polished UI, but the data is solid.
Sender Score by Validity
A third-party scoring service that pulls signals from a network of recipients. 0 to 100. Above 80 is healthy; below 70 means you have a problem.
Talos Intelligence
Cisco's reputation lookup. Quick check on whether your IP shows up in any spam classifications.
How to improve a damaged reputation
If your numbers are bad, here is the recovery sequence in order:
- Stop sending to anyone you do not have explicit consent for. Stop today, not next week.
- Verify your entire active list. Use MailoClean bulk; remove invalid and disposable addresses.
- Fix your authentication. SPF, DKIM, DMARC must all pass. No excuses.
- Send only to your most engaged 20% for two weeks. Anyone who opened in the last 30 days. Slowly expand from there.
- Drop frequency. If you were sending daily, drop to twice a week. Let engagement recover.
- Watch the metrics weekly. Postmaster Tools should improve within four weeks if you stick to the plan.
FAQ
How long does it take to build a good sender reputation?
Six to twelve weeks of consistent good behaviour from a new domain. There are no shortcuts.
Does verifying my list improve reputation?
Yes, indirectly. Verification cuts bounce rate, which is one of the largest inputs to reputation scoring. Combined with engagement-only sending, it is the fastest measurable improvement you can make.
Can I buy a "warm" IP to skip warm-up?
Technically yes, practically no. Most "warm IPs" sold on the secondary market are burned by spammers and have worse reputation than a fresh IP would.
Start with list hygiene
The fastest single improvement: verify your list today. Watching bounce rate drop below 1% feeds directly into reputation recovery.