I have 3 accounts configurated on my mail app. One icloud account and 3 other accounts.
I want an especific account to be my default account so when I press the write email icon always select by default my #2 account, but the app always takes the @me account to send the mail, I have to manually select the account to send the mail through #2 account.
Sometimes I forgot and the mail end up going through @me.com and the people reply my mail to that account, turns out o be a mess. I have look everywere for this option as the Iphone that is located under mail settings. But not in my OSx 10.8.2
Here's what I've found:
Open your mail application, and make sure you see your mailbox list on the left. (If you don't, go to the mailbox menu and click View > Show Mailbox List).
Look at your inbox in your mailbox list on the left. There's a flippy triangle next to "Inbox". Click the flippy triangle so that you see each individual account listed under inbox.
Finally, from that list of individual accounts, drag the one you want to be your default account to the top of the inbox list.
That should do it!