Your bounce rate tells you what share of sent emails failed to reach the intended destination.
It is one of the most practical health checks in email. If the number starts climbing, your list quality is usually slipping with it.
The formula
Bounce Rate = (Total Bounces ÷ Total Emails Sent) × 100
If you sent 5,000 emails and 150 bounced:
(150 ÷ 5000) × 100 = 3%
That gives you the total bounce rate.
Hard bounces vs soft bounces
It helps to split the number into two parts.
Hard bounce rate tracks permanent failures, such as nonexistent addresses or domains that cannot receive mail.
Soft bounce rate tracks temporary issues, such as a full inbox or a short-lived server problem.
Hard bounces deserve more attention because they are more closely tied to list quality and sender reputation.
A practical way to interpret the number
- 0-1%: very healthy
- 1-2%: still normal, but worth watching
- 2-3%: elevated and worth cleaning soon
- 3-5%: high enough to damage performance
- 5%+: a strong sign to stop and clean before the next major send
These are not universal laws, but they are useful operating ranges.
What can push the number up
Several things can move bounce rate in the wrong direction:
- old lists that have not been cleaned in months
- imported contacts from mixed or low-trust sources
- B2B lists with job-change churn
- typing mistakes collected through forms or manual entry
- stale segments that have not been touched in a long time
What to do if it is too high
If your bounce rate is climbing, the first response is usually not “send a smarter email.” It is “send to a cleaner list.”
That means:
- export the list or segment you plan to send
- run it through a validation workflow
- remove clearly undeliverable addresses
- review risky ones before the next campaign
MailCull is useful at that point because it gives you a practical status breakdown before you commit to the send.
The real goal
The point of measuring bounce rate is not the metric itself. It is using the metric as an early warning signal.
If the number trends up, your list quality is probably trending down. Catching that early is much easier than recovering after repeated poor sends.