Came across this, might work.
Marija, per Microsoft.com/Assistance...
Outlook does not prompt you to provide a Subject line. If you think you saw a prompt to provide a Subject line, you were looking at the basic email program Microsoft Outlook Express, which comes with Microsoft Internet Explorer.
You can create a toolbar button for a new blank email form and include a default subject, which can be changed, but if you forget then you still have the subject line filled in.
From the View Menu, Toolbars, Customize, the Commands TAB, drag NewMail message to the toolbar, with the Customize window still open, right click the new email toolbar button and select Assign Hyperlink at the bottom, choose email and then you will see a place to enter the subject. You do have to put some text in the email field but it can also be default to be replaced, but if you the same email frequently you might want to create a few buttons for each one with the e-mail already filled in.