Every email program will store all emails for an email account in a single file. We recommend customers ensure these files are regularly backed up in order to ensure they have a copy of their emails to ensure business continuity. The simplest way to backup these files are to export them from the email program however advanced users can select the file in use within their computer backup software. Please find below links to guides on how to export the email files so they can be stored securely: 

Microsoft Outlook 

Mac Mail