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 full
421 Service temporarily unavailable
450 Requested action not taken

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