How to choose the "From" account in El Capitan Mail when composing e-mail I use Apple Mail using two e-mail accounts (both IMAP but I don't think it really matters). Before El Capitan when composing an e-mail, one could choose the account the e-mail should be send from using a drop-down in the compose-window. However with the El Capitan update this dropdown is gone and there seems no way to select the account the e-mail should be send from after composing the e-mail.

The Mail settings do have an option to select the sending account. Here I can set it to one account or use the open mailbox as indication for which account to send mail from. 

Is there any way to switch the sending account after composing an e-mail in El Capitan?
Select your preferred email address in Preferences > Composing > Send new messages from:

If for some reason that doesn't work, try rebooting.