If it is sending to some addresses, but not to others, it is a server issue. you will need to contact the host to determine why the email is going to some addresses but the smtp server is not relaying to the others.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.