I no longer have the toolbar at the top of New Message (The one with buttons for Send, Add Attachments..). It is only missing in New Message, if I for example reply to a message, the toolbar is correct.
I can still send the message by selecting Message -> Send in the menu bar.
I have tried going to View -> Customize Toolbar, but it doesn't display any options.
I'm out of ideas. Searching the web I am only able to find the 'Customize Toolbar'-fix. I also haven't minimized the toolbar, as I've seen some solutions suggesting.