To disable all access/use of MailTips in Outlook 2013 a GPO or registry setting can be set.
User Configuration\Administrative Templates\Microsoft Outlook 2013\Outlook Options\Preferences\E-mail Options
Setting: Disable Mail Tips.
Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Options\Mail] "DisableMailTips"=dword:00000001
Source: Microsoft TechNet - Plan feature customizations in Outlook 2013