Bounce: An event that occurs when an email message cannot be delivered to a member due to a reason such as an incorrect email address, a full mailbox, or a problem connecting to an email server. In addition, the Groups.io system bounces messages containing new hashtags in a group in which the owner has specified the Hashtag Permissions setting, “Messages from members can only be tagged with existing hashtags, otherwise the message is bounced.” The system also bounces messages with attachments if the group's Storage Limit Reached setting is "Bounce Messages With Attachments" and the group has reached its storage limit.