Deliverability
Bounce
An email that cannot be delivered and is returned to the sender with an error message.
Definition
A bounce occurs when an email cannot be delivered to its intended recipient and is returned to the sender with an error message. Bounces are categorized as either hard bounces (permanent failures like non-existent addresses) or soft bounces (temporary issues like full mailboxes). Managing bounces is crucial for maintaining sender reputation - high bounce rates signal poor list quality to mailbox providers.
Examples
550 User not found (hard bounce)452 Mailbox full (soft bounce)421 Try again later (soft bounce)
Pro Tip
Remove hard bounces immediately and monitor soft bounces - if an address soft bounces repeatedly, treat it as invalid.