The Composer window is used to write new messages. It can be invoked from the Message menu or from the document icon on the Mail Reader window button bar. If you have not set the location of your signature file and you have Use a signature from file checked in the Composer tab of the Configure KMail... dialog, you will be prompted for the location of your signature file before the Composer window opens.
To write your message, fill in the appropriate fields in the Composer window. There are a variety of shortcuts to help you with writing your messages. The ellipsis buttons next to the To:, Cc:, and Bcc: fields will call up the address book so that you can select addresses from there.
When you start typing an address in the To:/Cc:/Bcc: fields, a popup will appear that offers matching addresses that have been used recently and matching addresses from your address book. Note that this auto-completion is case-sensitive, so if you type john, John Doe <doe@acme.com> will not show up automatically. If you don't like the automatic popup you can disable it by clicking with the right mouse button on the field and choosing a different completion mode.
Whenever you want to add more than one recipient in one of the fields, use a comma to separate each address from the next one. You may need to specify fully qualified addresses (i.e. user@domain.com) even for local users.
You can use the View menu to set up the header fields offered to you. When you are finished with your message, hit the Send button (the envelope) to queue or send the message. If you don't want to send your message yet, select Message->Save in drafts folder.
You can attach files to your message by using one of the methods below:
The Message Part Properties dialog will appear to prompt you for information about your attachment. The MIME-type and Name fields are automatically filled in with the appropriate values. Sometimes the MIME-type value may be wrong. You can then type in any content MIME-type or choose from the list of common MIME-types. You can also select an encoding method for your file from the list of encoding options (normally, the default value works fine).
Once a file is attached to your message, it appears in the Attachments pane at the bottom of the Composer window. You may remove, save, or get information about an attachment by selecting its name in the Attachments pane and selecting Remove, Save..., or Properties... from the Attach menu.
PGP/GnuPG keys may also be attached to your message by using the appropriate options in the Attach menu. PGP key attachments are handled like file attachments.