Deliverability
Soft Bounce
A temporary delivery failure, often due to a full mailbox, server issues, or message size limits.
Definition
A soft bounce is a temporary email delivery failure that may resolve itself. Common causes include full mailboxes, server downtime, message size limits, or greylisting. Unlike hard bounces, soft bounces should be retried. However, if an address consistently soft bounces over time, it should be treated as invalid.
Examples
452 Mailbox full421 Service temporarily unavailable450 Requested action not taken
Pro Tip
Most ESPs retry soft bounces automatically. Remove addresses that soft bounce consistently over several campaigns.