Hard Bounce vs Soft Bounce: What’s the Difference?
A hard bounce is a permanent delivery failure — the recipient address does not exist or the domain cannot receive mail — and the address should never be emailed again; a soft bounce is a temporary failure, such as a full mailbox or an overloaded server, where the message may succeed on a later retry.
Hard bounces
A hard bounce is a permanent failure. The mailbox does not exist, the domain has no mail server, or the server has explicitly and permanently rejected the recipient. The correct response is to stop sending to that address forever — a good platform adds it to a suppression list automatically so future sends are blocked before they leave the queue. Continuing to mail hard-bounced addresses is one of the fastest ways to wreck your sending reputation.
Soft bounces
A soft bounce is a temporary failure: a full mailbox, a server that is briefly down, a message that tripped a transient size or rate limit, or a greylisting delay. The message can succeed on a later attempt, so soft bounces are retried with backoff over a window — commonly 24 to 72 hours — and only promoted to a hard bounce (and suppressed) if they never clear.
Why the distinction matters
Treating the two the same is a costly mistake in both directions: suppress a soft bounce too eagerly and you drop deliverable recipients; keep retrying a hard bounce and you signal to mailbox providers that you do not clean your list. The split is what lets a sending platform protect reputation automatically without losing reachable contacts.
Keeping bounce rate healthy
Aim to keep total bounce rate under about 2 percent. A sudden spike almost always traces to one of three causes: a bad list import, a purchased rather than earned list, or a domain-authentication problem causing legitimate mail to be rejected. PostStack classifies every bounce, suppresses hard bounces automatically, and surfaces bounce trends so a spike is visible before it damages your reputation.
Frequently asked questions
Should I keep sending to an address that hard bounced?
No — never. A hard bounce means the address is permanently undeliverable, and continuing to send to it signals to mailbox providers that you are not maintaining your list, which damages your sending reputation. A good email platform automatically adds hard-bounced addresses to a suppression list so future sends to them are blocked before they ever leave the queue.
How many times should a soft bounce be retried?
A common pattern is to retry a soft bounce over a window of 24 to 72 hours with backoff, then promote it to a hard bounce (and suppress it) if it never clears. The exact number matters less than having a defined ceiling — endlessly retrying a soft bounce that has really become permanent wastes reputation and queue capacity.
What bounce rate is too high?
As a rule of thumb, keep total bounce rate under about 2 percent. Gmail’s sender guidelines and most reputation systems treat sustained high bounce rates as a strong negative signal. A sudden spike is usually one of three things: a bad import, a list that was bought rather than earned, or a sending-domain authentication problem.