Server-based rules versus On My Computer rules
There are two types of rules in Outlook for Mac: server-based rules and On My Computer rules.
Server-based rules If you are using a Microsoft Exchange account managed by Microsoft Exchange Server 2010 SP1 or later, you can use Outlook for Mac to create and edit server-based rules. In the Rules dialog box of Outlook for Mac, server-based rules are grouped by account under the EXCHANGE SERVER heading in the left pane. These rules run on the Exchange mail server, even when Outlook is not open. Because Outlook does not need to be open, server-based rules are useful if you access your account from more than one computer. One limitation of server-based rules are that they cannot carry out actions that require Outlook to be open, such as playing a sound.
If your account is managed by a version of Exchange earlier than Microsoft Exchange Server 2010 SP1, you can create or edit server-based rules by using Outlook Web App or Outlook for Windows.
On My Computer rules On My Computer rules, also called client-only rules, are rules that run only in Outlook for Mac. In the Rules dialog box of Outlook for Mac, On My Computer rules are grouped by account type under the ON MY COMPUTER heading in the left pane. You can create On My Computer rules for any account that you use in Outlook for Mac. Unlike server-based rules, On My Computer rules allow you to specify actions within Outlook, such as playing a sound.
If you have both server-based rules and On My Computer rules for the same account, server-based rules are always run first.