Have you ever raised money from someone that ignored your emails?
Is it worth continuing to email those that don't bother to even acknowledge you? I find it really hard to "spam" people but should I?
From their perspective, is there enough value for them to respond?
Is there too much friction involved if they do respond?
Can they respond? Are you sure? If your answer is a rapid "of course they can, don't be stupid" then reconsider and explictly verify its true. Then perhaps youll be better off than a certain CEO who said exactly that but didn't check and kept finding lower than expected conversions. Sales funnels aren't perfect and fail for lots of mundane reasons. Check again.