Soft bounce

A soft bounce is a temporary refusal. The receiving server answers with a 4xx SMTP code (for example 421, 450, 451 or 452), meaning 'not now'. Common reasons: the mailbox is full (4.2.2), the server is overloaded or rate-limiting your IP, greylisting, or a temporary policy deferral while the provider evaluates your traffic.

Your sending server is expected to queue the message and retry. If retries keep failing until the give-up time, the message is finally returned as undeliverable. Sending platforms usually count that as a soft bounce, and many convert an address to a hard bounce after several consecutive soft bounces.

One soft bounce is normal. A pattern is a signal: the same address soft bouncing for weeks is probably abandoned, and many soft bounces across one provider can mean that provider is throttling you because of volume or reputation. Google's guidelines suggest reducing sending volume when messages start being deferred.

When a server gives Skrap.ai a temporary answer during verification, the result is Unknown rather than a guess, and Unknown is free. Re-check those addresses later with the free email verifier or the API before adding them to a sequence.