Deliverability
What is Soft Bounce?
A temporary delivery failure that may succeed on a later retry.
A soft bounce is a temporary SMTP failure, signaled by a 4xx response, where the recipient server cannot accept the message right now but may later, for reasons like a full mailbox, a size limit, greylisting, or rate limiting. The sending MTA queues and retries soft bounces over a window before giving up and converting them to a permanent failure. Persistent soft bounces, especially deferrals tied to reputation or rate limits, often mean the receiver is throttling you.
Why it matters for cold email
In cold email a sudden rise in soft bounces or deferrals usually means a mailbox provider is rate-limiting your IP or domain because volume ramped too fast or reputation dipped, which is an early warning to slow down and revisit warming.
Related terms
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