What is a spam-complaint rate and what number is too high?

Your spam-complaint rate is the share of delivered emails that recipients mark as spam, and mailbox providers treat it as one of the loudest signals that your mail is unwanted:

• The hard ceiling - Google and Yahoo require bulk senders to stay under 0.3%, which is roughly 3 complaints per 1,000 delivered emails.
• The number to actually aim for - keep it under 0.1%; 0.3% is the line where filtering kicks in, not a healthy target.
• Why it is so unforgiving - one complaint carries far more weight than one open, so even a small spike can tip you into the spam folder.
• How to see it - Google Postmaster Tools reports your Gmail spam rate; most email platforms surface complaints too.

Make unsubscribing easier than complaining - a visible unsubscribe link keeps people off the spam button.