Am I doing this wrong?

I’ve seen a few Items that I was interested on Craig’s List recently so I hit the reply button and from the drop down menu I chose the “reply by email:” I copy and pasted the address and sent a message. I never heard back from any of the three people I mailed and am wondering if I’m doing something wrong? I’m new to Craig’s List so thought I’d ask here, is this normal? Do ad’s stay up long after their sold? Can they see my e-mail to reply to me if I don’t include it in my message? Thanks, N.