Your question is a bit confusing. What email provider are you using that you are trying to send and receive email from? Are you possibly talking about sending a private message like here on our forum and you called it an email?
Threads are new topics on a forum. The name of this thread is "email" (you named it that when you created it) What I am writing here is called a post. Posts are underneath a thread and talk about the topic of the thread. (the thread is the main topic)
Threads are not the same as emails and private messages on forums are not exactly like emails. (if you are talking about private messages) private messages can only be sent to and from members on a specific forum. Email questions members can only send messages to other email questions members. etc.
If you can be more specific with your questions, hopefully I can answer them.