Glossary Deliverability
Hard bounce vs soft bounce: what is the difference?
A hard bounce is a permanent delivery failure, such as an address that does not exist, while a soft bounce is a temporary one, such as a full mailbox or a server that is briefly unavailable.
Receiving servers return a status code. Codes starting with 5 (like 550, mailbox not found) are permanent; codes starting with 4 are temporary and may succeed later.
Never send to a hard-bounced address again. A soft bounce that repeats over several days should be treated like a hard one.
Why it matters
- Re-sending to hard-bounced addresses is one of the clearest signs of a careless sender.
- Telling the two apart avoids dropping good contacts after a one-off server hiccup.
- Hard bounces are the ones that count most against your bounce rate.
How Reach Crew handles it
When an email bounces, Reach Crew never picks that address again for that person, and bounces count toward the mailbox's health check, which pauses sending when they climb.
Related terms
- Bounce rate. Bounce rate is the percentage of sent emails that come back as undeliverable, usually because the address does...
- Email verification. Email verification is the process of checking that an email address is correctly formed, belongs to a domain...
- Sender reputation. Sender reputation is the trust that mailbox providers such as Gmail and Outlook place in a sending domain or...