To override the "From" address for OS X Mail, the help says the following: To choose an account for a message youre composing, click the From pop-up menu and choose an email address. If the From pop-up menu is not displayed, click the Customize pop-up menu in the header area and choose Customize. Select the checkbox next to From and then click OK. The trouble is that when I follow these instructions, there is no "From". What am I doing wrong?