Glossary: deliverability
What is email bounce rate?
Email bounce rate is the percentage of sent emails that were returned as undeliverable. You work it out by dividing the number of bounced emails by the number of emails sent and multiplying by 100.
Formula
Worked example
40 ÷ 2,000 × 100 = 2%
Bounce rate is bounced emails divided by emails sent.
The formula is simple. What matters is knowing which kind of bounce you are counting, because the two kinds call for different action.
A hard bounce is permanent.
The address does not exist or the domain is gone. Remove it at once and never send to it again.
A soft bounce is temporary.
The mailbox is full, the server is down or the message is too large. The address may work later.
Delivered is what is left.
Emails sent minus bounces gives emails delivered, which is the base for open rate and reply rate.
Here is bounce rate worked out for an invented company.
Imagine Farrowquay, an invented procurement software company. It sends 2,000 emails to an unverified list it has held for two years. It gets 240 bounces, so its bounce rate is 240 ÷ 2,000 × 100 = 12%.
Farrowquay then sends its next campaign to a verified list of 2,000 contacts. This time it gets 40 bounces: 40 ÷ 2,000 × 100 = 2%. Of those 40, 30 are hard bounces, which it deletes, and 10 are soft bounces, which it retries later.
Farrowquay's bounces per 2,000 emails
Keep bounce rate low in four steps.
Bounces are the most preventable problem in cold email, because they can be removed before sending.
The four steps in order
- 1Verify first
- 2Remove hard bounces
- 3Retry soft bounces
- 4Track by list
- 1
Verify first, then send.
Verification finds the addresses that would hard bounce before they do.
- 2
Remove hard bounces immediately.
Take them out of every list and campaign the same day.
- 3
Retry soft bounces a limited number of times.
If an address keeps soft bouncing, treat it as dead.
- 4
Track by list.
A list source with many bounces should be fixed or dropped.
Prymatica verifies every contact before sending, so your campaign reaches real, deliverable people, and monitors deliverability while it runs. See how Prymatica's cold email process works.
Teams make these mistakes with bounce rate.
Old lists are sent without checking.
Addresses decay as people change jobs. Last year's list bounces more this year.
Hard bounces stay in the list.
Sending again to an address that does not exist repeats the damage to sender reputation.
Email bounce rate is confused with website bounce rate.
The website measure is visits that leave after one page. It has nothing to do with email delivery.
These glossary terms sit next to bounce rate.
These Prymatica pages go deeper on bounce rate.
- How to Verify Email Addresses Before You Send (And Why It Saves Your Domain)
- The 5 Best Email and Phone Validation APIs in 2026 (Compared and Ranked)
- The Cold Email Metrics That Matter: Open, Reply, Bounce and How to Improve Each
- How Prymatica's cold email process works
- Lead generation agencies compared with Prymatica
Questions
People ask these questions about bounce rate.
How do you calculate email bounce rate?
Divide the number of bounced emails by the number of emails sent and multiply by 100. For example, 40 bounces from 2,000 emails is 40 ÷ 2,000 × 100 = 2%.
What is the difference between a hard bounce and a soft bounce?
A hard bounce is a permanent failure: the address or domain does not exist. A soft bounce is a temporary failure, such as a full mailbox or a busy server. Remove hard bounces straight away and retry soft bounces a few times.
Why does bounce rate matter?
Mailbox providers read a high bounce rate as a sign that a sender does not know its recipients. That lowers sender reputation, which pushes later emails toward spam, including the ones to valid addresses.
How do you reduce email bounce rate?
Verify every address shortly before sending, remove hard bounces the day they happen, stop reusing old lists without rechecking them and build lists from sources that keep their data fresh.
What counts as a bounce?
Any email the receiving server refuses or returns. The server sends back a message with a code that says why, and the sending tool sorts it into hard or soft. Emails that are accepted and later filtered to spam are not bounces.
Should bounces be counted against emails sent or emails delivered?
Against emails sent. A bounce is an email that was sent and not delivered, so sent is the only base that works. Open rate and reply rate then use delivered as their base.
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