Chronicle is a relational database which means many things are related to other things. For example, your email are related to a person, organization or job. Therefore, only a level 7 can permanently deleted an email from the system. All security levels can, however, remove an email from their list of emails on the main email tab. If you accidentally delete the wrong email from your list, you can get it back by clicking on the "deleted" folder listed on the left. This will show you the emails you have deleted so that you can undelete it.
If you do not see it, you may need to reset the Inbox by going to the Tools button in the Tool bar and selecting Reset Inbox.