The following options are available:
saving an email as a draft while you are composing the email
sending a saved email draft
How to save an email as a draft:
Click on the Save button on the Compose page.
Result: The email is saved in the Drafts folder.
Also see
Parent topic Organising E-Mail messages
How to send a saved email draft:
Open the Drafts folder.
Select an E-Mail.
Click on Edit draft in the tool bar.
Complete the entries. Click on Send.