Definition
Sender reputation is not a single score but a composite evaluation built from multiple signals that receiving mail servers continuously monitor. Each mailbox provider — Gmail, Yahoo, Outlook — maintains its own reputation algorithm, but the factors they evaluate are broadly consistent across providers.
A strong sender reputation means emails are accepted and delivered to the inbox. A weak reputation triggers filtering to spam, throttling or rejection.
Key Reputation Factors
| Factor | What Providers Measure |
|---|---|
| Complaint rate | The percentage of recipients who mark your email as spam |
| Unknown user rate | The percentage of addresses that do not exist |
| Engagement signals | Opens, clicks, replies and "not spam" markings |
| Sending volume consistency | Whether volume is stable or erratic |
| IP and domain age | How long you have been sending from the current IP and domain |
| Authentication | Whether SPF, DKIM and DMARC pass correctly |
| Blocklist presence | Whether your IP or domain appears on major blocklists |
| List hygiene | How quickly you remove invalid and unengaged addresses |
Best Practices
- Monitor your reputation through Google Postmaster Tools and Microsoft SNDS
- Keep complaint rates below 0.1% as a firm target
- Address reputation issues at the specific domain level — a problem at Gmail does not necessarily affect Yahoo
- Reputation builds slowly but can be damaged in a single campaign, making proactive hygiene essential
Related Glossary Terms
BIMI
BIMI (Brand Indicators for Message Identification) is an email standard that allows brands to display their logo next to their emails in supported email clients. It requires DMARC enforcement at quarantine or reject policy.
Bounce Classification
Bounce classification uses SMTP codes (550, 551, 552, 553, 554, 450, 451, 452) and enhanced status codes to categorise permanent and transient delivery failures.
Email Deliverability
Email deliverability is the ability to land in the recipient's inbox rather than the spam folder. It depends on sender reputation, authentication, list quality, and content practices.
DMARC Alignment
DMARC identifier alignment determines whether the domain in the From header matches the domains used in SPF and DKIM authentication. Strict or relaxed.
Acceptance Rate
Acceptance rate is the percentage of emails submitted for delivery that are accepted by the recipient's mail server, representing the first deliverability checkpoint before inbox placement is determined.
Email Acceptance Rate
Email acceptance rate measures the percentage of emails accepted by recipient mail servers versus total sent. It is a core deliverability metric that reveals whether your sending infrastructure is trusted by receiving servers.