It may help to know your email domain. That is, some email providers store the sent message in a predefined folder regardless of your setting, such as sentmail. If you sent the folder to be sent, you could end up with two copies. Knowing your setting for the sent folder may also be helpful. Thank you.

Hi David Thanks for the fast reply. My account is an IMAP with Gmail. On Gmail the folder is showing as "Sent" and not "Sent Mail". It's not a big deal anyway but just one of those things that annoy you sometimes. Thanks again David. Have a nice day.

A tip: when posting questions, it always helps to share some details. Now that I know you use gmail, I can advise that if you UNTICK saving the message in sent folder, that gmail does it anyway. That implies to me that you have it set to store the message, and that is causing you to have two copies. You can verify this by unticking the Sent folder setting, send a message, and then check the sent folder and the message should be there. See, you learned something today. :) Enjoy.

Gmail automatically copies sent messages to Sent Mail, so uncheck 'Place a copy in' in Account Settings, Copies & Folders. Unsubscribe Sent by right-clicking the account in the Folder Pane, Subscribe... In the same Subscribe window, unsubscribe the Drafts folder that appears near the top of the list and subscribe the Drafts folder under [Gmail], lower down. Set drafts to be saved in [Gmail]/Drafts in Copies & Folders, or Drafts on Local Folders if you don't need to access drafts on multiple devices.