A bounce (aka bounceback) is the e-mail message you receive if a sent message doesn't reach its destination. A bounce typically indicates that the message has not been delivered. MailUp takes care of automatically logging and cataloging bounces for you. In certain cases, it also reacts to them by performing actions such as unsubscribing a recipient whose email address generated a Hard Bounce (see definition below).

Here, let's look at how different types of bounces are defined. Note: these are pretty technical details. Unless you are interested in this topic, feel free to skip it (smile)