E-mail retention policies apply the maximum age of an e-mail to be kept in your mailbox before it is purged.

Please see below for a list of policies and the specific groups they apply to. Sub-folders and items inside of the folders listed below inherit the same retention time. It is suggested that you make any sub-folders you wish to save e-mails to inside of your "Mailbox" and not inside of your "Inbox", see the images above. All items not located inside a folder listed below will not be automatically purged and carry no retention limit.
Inbox - 13 months
Sent Items - 13 months
Calendar - 1.5 years
Deleted Items - 7 Days
Draft - 90 Days
Junk Mail - 1 Day
Outbox - 3 Days
Sync Issues - 1 Day