I’ve got some Quick Parts that I don’t use anymore but I’m not able to delete them. The option “Organize and Delete” is grayed out.
You must be composing in Plain Text format then. For some strange reason the “Organize and Delete…” option is not available when composing in Plain Text. Funny enough you are still able to add them.
Select the Options tab on the Ribbon to set the message format to HTML. Switch back to the Insert tab and “Organize and Delete…” will be available now.