In e-mail, a probe message is a type of bounce handling for e-mail address verification. It is commonly used in subscription-based mailing lists that easily become filled with invalid subscriber addresses. Once an e-mail has bounced from a specific address, a system will wait a specific amount of time then sends a warning message to the user. If the warning message bounces a probe message is then sent. If this also bounces the subscriber is then removed from the mailing list.