Outlook doesn't include a built-in method of creating an activity report, such as to show how many hours you worked on items marked with CategoryA and how much time was spent on CategoryB.
You can use a list view, copy and paste into Excel to do the calculations or use a third party reporting tool.
For tools to create reporting on Exchange server, see Exchange Server Usage, Reporting, and Analysis Tools.
The tools list on this page are used to create productivity reports.
OutlookStatView scans your Outlook mailbox, and display a general statistics about the users that you communicate via emails. For each user/email, the following information is displayed: The number of outgoing messages that you sent to the user (separated by to/cc/bcc), the number of incoming message that the user sent to you, the total size of messages sent by the user, the email client software used by this user, and the time range that you send/received emails with the specified user. Supports 32- and 64-bit Outlook.
VBOffice Reporter is an easy to use tool for data analysis and reporting in Outlook. A single click allows you to see the number of hours planned for meetings the next month, expenses for a specific project in the last month, and many things more. Features include the ability to create reports for all tasks, calendar, and journal items. Create a report with a single click and then sent via e-mail or open it in Excel. Trial available. Supports Outlook 2000, 2002, 2003, 2007, 2010, 2013.