Disappearing "From" field in Apple Mail In Apple Mail (7.3) on Mavericks (10.9.4), when I compose a new message, I cannot choose which of my two accounts to send from.  Bizarrely, when I open the New Message window, there is a From field, but it quickly disappears.  I'm including an animated GIF showing this behavior below.  How do I stop the From field from vanishing?
Open your preferences and go to "composing" amd change the setting for "Send new messages from:", close the preferences, quit mail, and then reset your preference to what you want.

If this doesn't work, make sure you don't have any Mail plugins installed.

Check the folder(s) if they exist:

$HOME/Library/Mail/V2/Bundles/
 $HOME/Library/Mail/Bundles/