When people mark you as spam.
WHY IT MATTERS MORE THAN UNSUBSCRIBES
A spam complaint is a direct signal to the receiving provider that your mail is unwanted.
Enough complaints and your mail stops reaching inboxes at that provider, including for people who want it.
THE ACCEPTABLE RATE
Very low. A fraction of a percent.
Your platform reports it. If yours is climbing, something is wrong.
THE COMMON CAUSES
Sending to people who do not remember subscribing Sending too often Sending content unrelated to what they signed up for An unsubscribe link that is hard to find A long gap since the last send, so people have forgotten you
REDUCING THEM
Double opt-in, so subscribers genuinely chose A visible unsubscribe link Consistent sending, so you are remembered Relevant content Removing long-inactive subscribers
IF THE RATE SPIKES
Stop sending and work out what changed.
Sending again into a complaint problem makes it worse.
THE PLATFORM'S POSITION
Services monitor this. A high rate can result in your account being suspended.
