Yahoo! Mail makes it “real simple” to add contacts automatically. Here are two ways to do it:

1. After you click Send, you’ll see a page that tells you who you just sent an email to (the “Message Sent” page). Under the person’s email address, you can check a box next to "Automatically add recipients to my Contacts (from now on)". By checking here, you’ll add the email addresses of all new people to whom you send emails into your Contacts. Nifty, huh? After checking the box, click OK. If you change your mind later and don’t want to add everyone to your Contacts, you can un-select the automatic function in the General category of Options. See #2, below.
2. Click Options in the upper-right corner of your Mail page.
   • From the list on the left side, click General.
   • Either check (to select) or un-check (to un-select) the box next to “Automatically add new recipients to my Contacts”. You’ll find this option at the top, after “When sending messages:”.