Hard bounces happen when the address is invalid, the domain does not exist or the server blocks you permanently. Soft bounces come from temporary issues such as a full mailbox, a server outage or a message that is too large.
Why it matters
Hard-bounced addresses should be removed immediately, because repeated sends harm reputation. Soft bounces can be retried a few times, then suppressed if they continue.
Common pitfalls and tips
Most email platforms label bounces automatically. Set rules so hard bounces are suppressed at once and repeated soft bounces are suppressed after a few attempts.
Example
An email to a former employee returns a hard bounce, so the address is removed. Another to a busy manager returns a soft bounce for a full inbox, and it is retried the next day.
How Leadvaro relates: Checking addresses first with Email Finder helps reduce both types.