Equal to or greater than 64 GB: Outlook retains 12 months of email.Between 32 and 64 GB (not inclusive): Outlook retains three months of email.Less than or equal to 32 GB: Outlook retains one month of email on your system.
It also uses that check to set a parameter in Outlook that determines how much mail will be downloaded to your local machine, based on the following disk sizes: When you install Microsoft Office, it checks your disk size to make sure you have enough space to install all of the applications.