But what if you use one of the "different" accounts more often than the account suggested by Mac OS X Mail as the default? Make the account you use most often to send messages the default!
Specify the Default Account in Mac OS X Mail
To specify a default email account in Mac OS X Mail:
- Select Mail | Preferences... from the menu.
- Go to the Composing category.
- Select the desired account under Send new messages from: (or Send new mail from:) (under Addressing:).
- Close the preferences window.
Specify the Default Account in Mac OS X Mail 1
To set the default account in Mac OS X Mail 1.x:
- Select Mail | Preferences... from the menu.
- Go to the Accounts tab.
- Click on the account you want to make the default and
- keep the mouse button pressed.
- Drag the account to the top of the accounts list.
- Release the mouse button.
Mac OS X Mail uses the topmost account in the account list as the default for outgoing messages. Of course, you can change the complete order of all accounts using this drag-and-drop method. The individual account's folders under Inbox, for example, are also sorted in this order.

