What is a bounce rate?
Bounce rate is the share of sent messages that were rejected, expressed as a percentage. Most mailbox providers begin throttling above roughly 2%, and sustained rates above 5% put a sending domain at real risk. Hard bounces count against reputation far more heavily than soft bounces.
The arithmetic is simple — bounces divided by messages sent — but the threshold is what matters. Below 2% is healthy. Between 2% and 5% is a warning that the list has aged or was acquired rather than earned. Above 5%, providers start treating you as a sender who does not maintain a list, and that judgement is slow to reverse.
Hard and soft bounces are not equivalent. A full mailbox resolves itself; an address that does not exist never will, and repeatedly sending to it is the specific behaviour that damages reputation.
The useful thing about bounce rate is that it is entirely predictable before a send. Verification tells you the rate you would have had, which turns a reputation problem into a filtering step.
Last reviewed 2026-09-11