What is an acceptable spam complaint rate?

A spam complaint is when a user clicks the "This is Spam" or "Report Junk" button in their inbox. It is the single most damaging negative signal a sender can receive, as it tells the mailbox provider your mail is unwanted.

While the only truly acceptable rate is zero, the universal "danger" threshold for most mailbox providers is 0.1% (or 1 complaint per 1,000 messages).

If your complaint rate consistently exceeds this 0.1% line, providers will lose trust in your domain, and your messages will be routed to the spam folder. It is the "red line" on your ship's radar; crossing it means you are sailing directly into a storm.