I suggest using a common sales technique. End the email with a question instead of an open statement that requires no response. The question can be as simple as

I suggest using a common sales technique. End the email with a question instead of an open statement that requires no response. The question can be as simple as "Does this work for you?" By using a question your assuming / prompting a response. It may not always be the response you're looking for but at least you'll know one way or the other. The OP's idea of proposing two solutions is good too, even if there is one real solution. You're allowing the client to make a decision, even if it's a forced one. It lets them feel in control. Give them two solutions and then ask something like "Which would you prefer?" You're almost guaranteed an answer. When I get a new lead for a project I know nothing about (either incoming or outgoing) I usually do a very brief one or two sentence intro and end with "How can I help?" It's similar to "Let me know if I can help" but requires a response.