Emails are automatically saved while being edited. Lead Liaison provides a lock/unlock feature to prevent errors caused by multiple users editing the same email. When an email is being edited by an existing user a new user attempting to edit the email will be prompted with an option to unlock the email, ending the other user's session, or exit the edit attempt.
Once the user editing an email exits edit-mode (clicking exit, going to the send or test step, etc.) then other users may edit the email and will not see any lock prompts.