Spam Complaint Rate
Spam complaint rate is the percentage of delivered emails that a recipient marks as spam or junk, calculated by dividing complaints by emails delivered. Mailbox providers such as Gmail and Outlook use this rate as one of the strongest signals when deciding whether to trust future sends from a domain.
Why it matters for outbound teams
Even a small increase in spam complaints can trigger a sharp drop in inbox placement across an entire sending domain, affecting every mailbox that shares it. Providers generally treat anything above 0.1 percent as a warning sign and anything above 0.3 percent as a serious problem. Keeping this rate low requires relevant targeting, honest subject lines, and an easy way for recipients to opt out.
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