The K Desktop Environment

4.4. Miscellaneous Tab

Empty Trash On Exit

The trash folder is cleared of messages when you quit KMail if this option is selected.

Send Mail in outbox Folder on Check

All messages queued in the outbox folder will be sent whenever you check your mail.

Use external editor instead of composer

If you don't like the Composer you can use any editor. Note that the Composer window will still open and the external editor will open as soon as you type just one character in the body of the message.

New Mail Notification

This let's you configure actions for the arrival of new mail. Note that automatically fetching mail can be configured in your account settings under Receiving Mail.