The hard part of bounce handling is matching up a bounce message with the undeliverable address that caused the bounce. If the mailing list software can see that a bounce resulted from an attempt to send a message to user@example.com, then it doesn't need to understand the rest of the information in the bounce. It can simply count how many messages were recently sent to user@example.com, and how many bounces resulted, and if the proportion of bounced messages is too high, the address is removed from the list.