Sender reputation for beginners: a plain-English guide

The one-sentence version#

Sender reputation is the score mailbox providers assign to a sending domain and IP based on complaint rates, bounce rates, engagement, spam-trap hits, and authentication history. It determines whether mail is delivered, filtered, or rejected.

Why you should care#

Reputation is the dominant factor in inbox placement. Content matters far less than the trust a provider has in your domain.

The mental model#

Think of sender reputation as a contract between you and the mailbox providers receiving your mail. You publish or configure something they can check; they check it on every message; the result feeds their decision about where your message lands. Everything below is about making that check pass consistently.

Your first setup, step by step#

1. Register in Google Postmaster Tools and Microsoft SNDS to see your domain and IP reputation directly.
2. Keep spam complaints below 0.1% (Gmail's threshold is 0.3% for enforcement) and hard bounces below 2%.
3. Segment by engagement and stop sending to contacts inactive for 90+ days.
4. Authenticate with SPF, DKIM, and DMARC so reputation accrues to your domain rather than a shared IP.
5. Ramp volume gradually after any pause longer than two weeks.

Words you will see#

• Mailbox provider: Gmail, Microsoft, Yahoo, Apple, and the corporate gateways that decide where mail lands.
• Authentication: proof that a message is from who it says it is (SPF, DKIM, DMARC).
• Reputation: the provider's running score of your domain and IP.
• Placement: whether a message reaches the inbox, spam, or is rejected.

Common mistakes#

• Buying or scraping lists, which seed spam traps into your database.
• Blasting an entire list after months of silence.
• Ignoring Postmaster Tools until placement has already collapsed.

Frequently asked questions#