You can compose and send your email messages as soon as you write them, or you can compose a draft and return to it later to finish and send.
The first step to composing a new message is
to click 
on the toolbar to open a blank compose page. You can also right-click
the name in the Sent By section
of an email and select New Email,
to open a blank compose page. Depending on your Mail
preferences, the blank compose page opens in the Content pane or opens
as a separate compose window.
In the Compose window, you enter the email address of the person or persons to whom you are sending the message in the To: field. You can click To to look up a person's email address in order to search through your contacts . To add BCC addresses, click Show BCC next to the Cc: text field in the message header.
You can either compose your message in HTML or in plain text. The default format is configured in your Preferences, General tab. To quickly change the format for this message only, click Options on the compose toolbar and select either HTML or Plain Text.
Format As HTML lets you format your message with different font styles, create tables, add color, and insert hyper links.
Format As Plain Text produces text with no style or formatting. Any computer can read this type of message.
You can attach files, including pictures, documents, spreadsheets, audio files to your message.
Click from the toolbar. The compose page is displayed.
If you are not using the default identity, in the Account drop-down list, select the identity (also known as persona) to use.
Complete the address, subject line, and body text as needed.
If you supply a first and last name that is not in the form of a valid Internet address (name@domain.com), a confirmation dialog appears advising you that the address does not appear to be valid. You can choose to send the mail anyway, even though it may not be deliverable.
Enter the body of the message in the text box below Subject.
To check the spelling in the message, click Spell Check.
To add an attachment, click 
.
Add your signature. If you have different accounts set up, in the Accounts drop down, select the email address to use for this email. If you have signatures style defined for the account, click Signature on the Compose toolbar to add that signature.
Click Send to send the message.
If you don't want to send the message immediately, click Save Draft. The message is saved in the Drafts folder.