Mail Bounces

A bounce, in general, is when an email is rejected for delivery for some reason.  The reason is usually apparent in the description of the bounce type.  Bounces are then broken out into two other classifications:  soft and hard.  Each of these types of bounces is used by various remote sites to better manage their email infrastructure.  Even though there are two different types, a bounce is a bounce is a bounce.  In other word, the email was rejected for some reason.

• Industry standard terminology is that a “hard bounce” is a delivery attempt that failed, and will never succeed without manual intervention. They’re what are known as 5xx rejections when they happen during the SMTP transaction, as the error code is in the range 500-599.

• A “soft bounce” is a delivery attempt that failed, but for a transient reason. The delivery will be retried automatically by your smarthost. They’re often called 4xx rejections, as when they happen during the SMTP transaction the error code is in the range 400-499. These happen all the time, and you don’t need to worry about them, they’ll be handled by your smarthost (and eventually escalated to a hard bounce if the delivery keeps failing).