I've read through as many posts as I could and haven't found an answer. Here are some specifics for this installation.
Host: Yahoo
Admin email: @billyjdjs.com
So the user notifications work perfectly, no matter what email is used there. @hotmail.com or @billyjdjs.com. The administrator notifications will not work with any I have tried, @hotmail.com, @billyjdjs.com or @yahoo.com.
I tried the wp-email-smtp plugin and didn't get anywhere. In fact, I couldn't get it to send a test email using SMTP. But the PHP mail works fine.
If I put the Admin email in the BCC of the user notification section, I get the form with no trouble. Also, if I put the Admin email in the BCC of the admin notification section I get the form sent to the Admin email. It's just something about the Send to Email in the Admin section that is giving me trouble.
I saw a thread where someone had the same issue and he said he tweaked a setting and everything worked fine. The problem is he didn't say what he tweaked.