Make It Multimodal

When you send a proposal, your best bet is to make it multimodal.  If you send an email, accompany it with a voicemail to check in.  Say, "Hello, _____.   I just sent you the proposal as promised.  Please confirm that you've received it.  If I don’t hear from you sooner, I'll get back with you in a couple of days so we can chat through it."