Add Contacts automatically adds e-mail addresses to the contact folder when you reply a message and/or send a new message. This will help you avoid losing addresses of people you correspond with. Moreover, the collected addresses can be used for mail filtering. For example, you can use the Rule Wizard to have messages from certain senders (whose addresses are there in the address book) placed in a separate folder to ensure that their message will be dealt with greater priority and no important messages will be lost with deleted spam. Some spam filters also check the contact folder to rule out erratic response for recognized senders.