The mail flow tab is one of the other important areas of Exchange Online; it allows the administrator to shape where mail goes, who it goes (or does not go) to, and to trace it when there are problems.
Most of us are familiar with rules in Microsoft Outlook, such as forward all mail coming from [email protected] to [email protected] unless the subject message contains 'Re' or other such algorithms. Many of us keep our mailbox uncluttered (or try to, anyway) and organize mail using such rules.
You can establish rules here on the server as well, but the functionality is somewhat more limited than the rules that users can create for themselves. There are things you can do here that are technically rules, but so commonly performed by administrators that they've actually been given their own entry in a drop-down menu, such as Apply disclaimers... or Generate an incident report when sensitive information is detected...:
Rule creation