Diane wants to be able to save her email messages from Yahoo Mail locally to her computer as a form of backup. Leo suggests using an email client, and he recommends Mozilla Thunderbird. This program stores email in a very standard mbx, or mailbox format, that other programs can also understand. That way, if Thunderbird were to go away, Diane would be able to easily be able to still look at her messages with any text reader.
Diane will have to figure out the POP settings she will use to access her Yahoo Mail through Thunderbird. She'll also have to enable POP mail access from her Yahoo Mail account online. One option she should make sure to leave checked is "leave mail on server," unless she wants to have her email deleted online when it's downloaded to Thunderbird.