A computer-implemented method for managing failure messages for email messages, the method comprising: receiving, in a computer, a failure message from an Internet service provider (ISP) as a result of a failure by the ISP to deliver an email message to an email address associated with the ISP; classifying, using a processor of the computer, a failure type of the failure using the failure message; and determining, using the processor, whether the email address is invalid based upon the failure type and based upon the associated ISP. view more