In Outlook 2003 and above (I don't know about older versions), one could go to
View / Arrange By / Custom / Other Settings and select Hide header information. In Outlook 2010 also it was accessible via
View tab / View Settings / Other Settings, although it was admittedly buggy:
Unfortunately in keeping with Microsoft's love for feature removal both in Windows and Office, this is what you get now:
Microsoft confirms that this useful feature has been removed. Other options in the dialog above such as adding Grid Lines betweens mails in the folder listing pane, turning off Group Headings and Always use compact layout might be of interest however.
There is an irritating expandable Social Bar that is displayed at the bottom of the Reading Pane:
To disable it:
Go to the File tab:
Click on Options:
Select Add-Ins, then COM Add-ins from the Manage drop-down and then Go:
Uncheck Outlook Social Connector 2013 and OK your way out:
The Navigation Pane at the bottom of the Outlook window by default displays 4 items - Mail, Calendar, People and Tasks. Here's how to modify it:
Click on the ellipsis and then Navigation Options from the pop-up menu:
Now you can customise how the pane looks, by changing the the maximum number of visible items, the order of items on the pane, or switch to compact mode:
Here's what it looks like with more items visible:
Here's what it looks like with Compact Navigation selected:
AFAIK you cannot remove the Reply/Reply All/Forward buttons from the Reading Pane:
Clicking those by default leads to the new Quick Compose / Inline Reply feature being activated. Here's how to turn it off if you always want to reply in a new window by default:
Click on File / Options / Mail:
On the right side of the window, scroll down to the Replies and forwards section and uncheck the Use inline replies when replying or forwarding option:
Outlook displays one line of each mail by default in the folder listing pane. For a more compact listing you can turn this preview off:
On the View tab, click on the Message Preview option to display the following pop-up menu:
The purpose of each option should be obvious.
You might see the following dialog box on changing this setting:
Select as required to make this a global/local change.
To turn off the Reading Pane altogether, on the View tab click on Reading Pane and then select Off from the pop-up menu:
This is a per-folder setting.