If you want to save a message that you do not want to send yet, you can save a draft of the message. To save a draft of a message that you are composing, choose File -> Save Draft. The message is saved in your local Drafts folder.
To continue to compose a draft message, open the message from your local Drafts folder, then complete
To send a draft message, open the message from your local Drafts folder. Complete the message in the composition window, then choose File -> Send.