Mail.app extension to avoid sending email from the wrong account? I have recently starting using Mail.app with two email accounts (work and home).  Every now and then I send email while having the wrong folder selected, and the default "from" account will be not what I expect.  Are there any extensions or tips to make the currently selected "from" jump out at me in the compose window if it's not the 'default' from address?  In other words, 99% of the time, I use my main account, but if I accidentally open a compose window with the alternate account, I'd like a different background color in the compose window, or some big flashing icon or something.  The problem case happens because I was reviewing a folder in the non-default account.  Any ideas?
Mail > Preferences > Composing