What to do with Email Address Only contacts?

Hi,

I have 13k email address only contacts on my database and I'm putting them on nurture soon but do you have any other recommendations on what to do with it aside from the usual nurture campaign?

I'm hoping I could get these contacts to download white papers or at least opt-in from our newsletters, but so far, there are no engagement from them and I don't want to lose hope that I could get them engaged with my campaigns.

This will be the last straw before I completely scrub them off our database.