/ Glossary — Reputation & Bounces
What is a soft bounce?
A temporary delivery failure that may succeed on a later retry — a full mailbox, a server that's down, a message too large. Here's how it differs from a hard bounce and when a soft bounce becomes a real problem.
/ Definition
A soft bounce is a temporary email delivery failure — the message couldn't be delivered right now, but the condition causing it may clear, so the sending server keeps trying. Common causes are a recipient mailbox that's full, a receiving server that's temporarily down or overloaded, or a message that's too large for the recipient's limits. Unlike a hard bounce, which is permanent, a soft bounce is provisional.
When a message soft bounces, the sending server doesn't give up immediately. It queues the message and retries on a schedule, typically over a day or two, in the hope that the temporary problem resolves. Many soft bounces eventually deliver on a later attempt — but one that never clears within the retry window ends up undeliverable, and an address that soft bounces again and again is behaving like a dead one.
/ In practice
When does a soft bounce matter?
A single soft bounce is rarely something to worry about — temporary conditions are part of normal email, and the retry system exists precisely to handle them. What matters is the pattern. An address that soft bounces consistently across multiple sends isn't experiencing bad luck; it's signalling a deeper problem, whether that's a permanently full abandoned mailbox or a receiving server quietly throttling your mail because of a reputation issue. A rising soft-bounce rate across your whole list is often an early warning that providers are starting to defer your mail, which is why it belongs on your deliverability monitoring dashboard.
How should you handle them?
Don't suppress an address on its first soft bounce — it's almost certainly still valid. Instead, track soft bounces per address over time and apply a threshold: after a set number of consecutive soft bounces with no successful delivery in between, treat the address as effectively dead and move it to a suppression list. Just as important is reading soft bounces in aggregate, because a sudden cluster of them concentrated at one mailbox provider usually means throttling rather than full inboxes — a reputation signal you want to catch early rather than a list-hygiene one.
/ Related terms
A rising bounce rate is a signal. We catch it before it costs you.
Soft bounces clustering at one provider often mean throttling — the kind of early signal continuous monitoring surfaces and we act on. Bring us your sending and we'll keep delivery steady.
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