Also known as: Temporary Bounce
A temporary delivery failure caused by a transient issue, such as a full mailbox or a server that is briefly unavailable.
A soft bounce is a temporary delivery failure. The address is usually real, but the message could not be delivered right now — common causes are a full mailbox, a message that is too large, a server that is down for maintenance, or greylisting, where the receiving server deliberately defers first-time senders.
Because the problem is transient, most email service providers automatically retry soft bounces for a period (often 24–72 hours) before giving up. If an address keeps soft-bouncing across multiple campaigns, many senders treat it as a hard bounce and remove it.
Soft bounces are normal in small numbers. They become a problem when they cluster — a spike can indicate a reputation issue rather than individual mailbox problems.
A permanent delivery failure that happens when an email is sent to an address that does not exist or cannot receive mail.
An anti-spam technique where a server temporarily rejects mail from unknown senders, expecting legitimate ones to retry.
The percentage of sent emails that could not be delivered and were returned by the receiving server.
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