"Enable Content" pop-up after creating macro

Hey everyone,
I have just created a macro so that a message pops up before the user closes the workbook. However, now they have to click "Enable Content" in order for that macro to run. The departments I am sending this file to will not click on that button and will therefore not see my message. I understand that you do not want to enable "automatically run macros" and that is not what I want to do. But even if I did want to do that the choices in that section are grayed out.

How else can I have the macro run without the receiver having to click on "Enable Content"? Thanks in advance for your help.