Anyway, if you are plagued by a DM box overflowing with useless auto DMs from marketers who can't grasp how to use Twitter effectively, I found a little tool that deletes the little blighters in a flash (well, a few seconds anyway)
Go here The DM Whacker,
Drag the bookmarklet: 'DM Whacker' onto your bookmark bar and navigate to your DM page. Click the new bookmark and a menu appears in the Twitter sidebar. Choose your options and zap them! Careful though, there's no recycle bin, once they're gone, they're gone!
Enjoy your clutter-free DM box.