Spam complaint rate

When a recipient presses "Report spam", the mailbox provider counts it against the sender. It is the most direct signal providers have that mail is unwanted, which is why their limits on it are so low. Gmail's sender guidelines ask senders to keep the spam rate reported in Postmaster Tools below 0.10% and never to reach 0.30%; Yahoo's best practices set the line at 0.3%.

In outbound, complaints come from people who did not expect to hear from you and see no easy way out. They fall when the list is narrow and relevant, the sender is clearly identified, the email is short and honest, and stopping is easy: a plain unsubscribe link, and a reply of "no thanks" honoured at once. Because a few complaints can matter at low volumes, a campaign that draws one should be paused and looked at rather than allowed to continue.

• In Outlevo: A campaign pauses itself above 3% hard bounces or 5% unsubscribes over its last 200 sends, or at a spam complaint.

Sources: Gmail email sender guidelines (support.google.com, checked oct 22, 2026); Yahoo sender best practices (senders.yahooinc.com, checked oct 22, 2026).