How do I set one address as the default address I’m sending from?

Here’s how:

Click Options in the upper-right corner of the page and select Mail Options.
Under “Management”, click Mail Addresses.
From the list of addresses, click once on the one you’d like to set as the default send-from address.
That account info appears in the box on the right. In that box you’ll see a Make Default link. Click it!
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)

Tutorials