Here’s how:

1. Click Options in the upper-right corner of the page.
2. Under “Management”, click Mail Addresses.
3. From the list of addresses, click once on the one you’d like to set as the default send-from address.
4. That account info appears in the box on the right. In that box you’ll see a Make Default link. Click it!
5. At the bottom of the page, click Save Changes. Now wipe the sweat off your forehead because we all know what a workout that was. ;o)