Prospect leads are different from customers.  Prospects have not had a transaction with you.

They probably are just forming an opinion about your business.  They should treated differently than customers.

By segmenting your email lists between prospects and customers, you can talk to them in a different manner.

Talk to your prospect leads in an inviting way.  Give them reasons to come meet you.  Invite them to open houses.

They should meet your staff.  No pressure here, though.  Listen to their needs.  There is a reason God gave us 2 ears and 1 mouth, right?

Once you know their needs, fears and desires, you are able to serve them much better.

When the time comes that they purchase from you, move them over to the customer email list and delete them from the prospects list.

Mission accomplished.