Exchange Online which comes bundled with Office365, has a very unique feature for Email compliance. It is called Email Retention Policies

Email Retention Policies

It offers two types of policies: Archive policies and Delete policies. Exchange Online offers retention policies to help organizations reduce the liabilities associated with email and other communications. With these policies, administrators can apply retention settings to specific folders in users’ inboxes. Administrators can also give users a menu of retention policies and let them apply the policies to specific items, conversations, or folders using Outlook 2010 or later or Outlook Web App.

Exchange Online offers two types of policies: archive policies and delete policies. Both types can be combined on the same item or folder. For example, a user can tag an email message to be automatically moved to the In-Place Archive in a specified number of days and deleted after another span of days.
Have a look at some of the Retention Policies that you may use as is shown in the snapshot below:

Business Use Case

Let take an example . Assume you receive many newsletters every day . So you can have this rule that all newsletters should go to your Newsletter folder . That rule will save you time to manually move the item to the Newsletter folder. You can have a glance at them as per your convenience. You can also apply a retention policy to your Newsletter folder. The policy is “6 months deletion” . What happens is that as soon as any item in this folder crosses 6 months, it gets auto deleted. Have a look at the screen shot below :

The newsletter folder is highlighted on the left. And the folder policy is highlighted on the right. And it says 6 months.

With Outlook 2010 or later and Outlook Web App, users can apply retention policies to folders, conversations, or individual messages. They can also view the applied retention policies and expected deletion dates on messages. Users of other email clients can only have email messages deleted or archived based on server-side retention policies set by the administrator.
So by making intelligent use of Retention policies, you can manage your email system much better and at the same time ensure compliance also.
To know more about other Email Management  features, visit our Email Management Solution page.