Below is a list of features removed or drastically changed in Outlook 2013. Some features, like Suggested Contacts, were disliked by a large number of users, others, like the To-Do Bar and Windows Search, were replaced by a less functional feature (Pinned Peeks) or removed completely.
|/Cleanfreebusy switch and code||Users can no longer start Outlook using the /cleanfreebusy switch and will receive this error message if they try to use the switch: "Cannot start Microsoft Outlook. The command line argument is not valid. Verify the switch you are using."|
This switch was used to remove free/busy data from the Public Folder Free/Busy, which is no longer supported in Outlook 2013. (This is one of many reasons why Outlook 2013 won't work with Exchange 2003.
|Activities tab||The Activities tab was replaced by the Outlook Social Connector and displays in the People pane. Contact Activities functionality was reduced in Outlook 2010.|
|AutoPreview unread messages||AutoPreview (3 line preview) was removed and replaced by Message Preview, which allows you to display one, two, or three lines in the message list. Look for the Message Preview button on the ribbon.|
|Calendar Publishing to Office.com||It's no longer possible to publish calendars to Office.com. You can publish calendars to other Web-DAV servers. Exchange Server users can use Exchange Calendar Publishing, while other users can use a service such as Hotmail or other Web-DAV servers to share calendars.|
|Color categories "quick click"||Categories quick click button in the Compact message list was removed. Color categories are displayed in message list, next to the flag quick click, but you need to apply the categories using keyboard shortcuts, the Category command on the ribbon, or by right-clicking on the message. If you use the single line message list (common with the reading pane turned off or positioned on the bottom) the click click is available. Why was it removed from the Compact list? According to their data, it was used by less than 1% of users. (I'm shocked it was that low.)|
|Contact Linking||The ability to link Outlook items to Outlook contacts using the Contacts button on a form or Options dialog was removed. Contact linking was used only to display information in the Contact's Activities tab, which was removed also.|
Use the Outlook Social Connector and the New Person Card instead. See Show Contact Linking fields in Outlook 2013 to enable the showcontactfieldobsolete registry value using Group Policy.
|Deliver Exchange mailboxes to PST||The ability to have Exchange accounts delivered to PST files was removed. Users will need to use Rules to move mail from an Exchange mailbox to a PST. Why was this changed? Because delivering mail to a PST breaks Exchange mailbox functionality.|
|Dialup/VPN Options||Application level dial-up and VPN options were removed as these are available as part of the operating system. Outlook uses the Internet (or VPN) connection the computer is using.|
|Direct Booking||Direct booking of calendar resources is not supported. Use the Exchange Availability service and free/busy for resource calendars. Resource mailboxes provide a better range of features and simplify resource mailbox management with server-side administration.|
|Exchange "offline" mode||Offline mode is a legacy method for offline connections to Exchange Server. It was removed from Outlook 2013. Use Cached mode instead.|
|IMAP Sent and Delete user configuration||The ability to select a Sent or Deleted item folder in IMAP accounts (added in Outlook 2007 and Outlook 2010) was removed from Outlook 2013. Instead, Outlook 2013 uses XLIST command to ask the IMAP server which folders to use. If an IMAP server doesn't support XLIST, Outlook puts sent and received items in the local data file. Use a rule or VBA to move items.|
|Import/Export to other file formats||Import/export of Outlook data to legacy file formats was removed from Outlook 2013. You are limited to using CSV or Outlook data file (pst).|
|Journal||The Journal was removed as a top-level module. This includes auto-journaling of Outlook items and Office documents. The Journal folder is available and you can create new journal items but the functionality is severely reduced. See Making the Journal work in Outlook 2013 for tips if you are still using the journal.|
|Meeting Workspaces||The Meeting workspaces feature is not available in Outlook 2013. The command was removed from both the Quick Access Toolbar and the Ribbon. Why was it removed? Very few people used it.|
|Notes customization||Notes are available only in yellow color and the medium size. Notes can be resized on the screen and will retain that size; only the default note size is affected. As in previous versions, applying a color category to a note changes the note color, only the default colors of pink, green, blue etc were removed.|
|Outlook Links Collection||Gone is the Links Collection object model and functionality was removed from the user interface.|
|Outlook Mobile Service (OMS)||Support for the Outlook Mobile Service protocol, which is used for sending and receiving text messages from Outlook, was removed due to low usage.|
|Public Folder Free/Busy||Public Folder Free/Busy feature was replaced by the Exchange availability service. See Understanding the Availability Service for more information. This is one reason why Outlook 2013 does not work with Exchange 2003.|
|Search through Windows Shell||In Office 2013, Outlook items do not display in Windows searches (for example, searches from the Start Menu or Windows Explorer). You need to search within Outlook 2013. See Searching for Outlook items in Windows 8 for more information.|
|Suggested Contacts||Suggested Contacts was introduced in Outlook 2010 to automatically keep track of everyone the user sends a message to, but who isn’t already in Outlook contacts.|
In a clean Outlook 2013 installation, Suggested Contacts is no longer available, the folder is not created, and no suggested contact items are created. In an upgrade to Outlook 2013, this folder is visible, however no new suggested contact items are added to the folder and it can be deleted.
|ToDo Bar||The To-Do Bar was replaced by Pinned Peeks. No, it's not quite the same and has less functionality. Using the Calendar Peek in Outlook 2013|
|User Datagram Protocol (UDP)||The UDP functionality that was provided by UDP is replaced with an asynchronous notification method. In earlier versions of Outlook the feature was used for new mail alert results and for folder updates.|
Outlook features we loved (or hated) that lasted just two versions
Outlook 2013 deprecated features and components
What's new in Outlook 2013 (TechNet)
Changes in Office 2013 (TechNet)