Server-side vs. Client-side Rules

A new Outlook 365 Exchange Online user is struggling with rules.

I'm trying to figure out the hierarchy actions of the rules. I need to have email messages with exact subject detail sent to a specific folder. I also noticed that some rules are server based and are done first before leaving the 'cloud' and that rules on OWA seem to conflict with those set in Outlook.

If Outlook is open, the rules should be processed in the order listed, but when Outlook is closed, the server rules are applied. When you create rules in OWA, only server rules are supported.

Rules that have actions that require Outlook are client side rules and only run if Outlook is running. This includes moving messages to local pst files, adding a category or a flag. If a server rule moves a message when Outlook is closed, the client side rules that might apply to the message won't fire.

Suppose, for example that there are two rules. The first moves any message with "abc" in the subject to Folder A and the second rule moves messages sent from "microsoft.com" to Folder B. What happens if I receive a message from Microsoft that has "xyz" in the subject?

In this case, it depends if you are using Stop Processing with the first rule. When the message arrives, it's processed by the rules in the order they are listed and the message is checked against all rules unless a rule includes Stop Processing. With the Stop Processing action added, when a message matches the rule, Outlook stops looking at the remaining rules and moves on to test the next message. If you don't want a copy of the message in Folder A and one in Folder B, you need to use Stop Processing in Rule 1.

Client or Server Rules?

You can divide rules into two types - server-side and client-only. Server-side rules are handled entirely by the Exchange Server, independent of the state of the Outlook client. Client-only rules do not execute until the user who created the rule logs in to the Outlook client with the same profile used to create the rule.

Whether a rule is server-based or client-based depends on the exact conditions and actions for that rule.

Certain rules are always client-only - those that involve some element from the Outlook client that does not exist on the Exchange Server. The following table classifies these according to whether they depend on Outlook features, client files or the mail profile. The last group contains something of a surprise: A rule to copy to a public folder fires only when the client is logged in with the profile that created the rule.

TIP: Try forwarding the message to the public folder instead. That rule always fires on the server.

When you create a rule, the Rules Wizard stores the rule settings (conditions, actions, and exceptions) in a .rwz file with the same name as the user's profile. For rules for incoming messages, it also stores that information in the Inbox folder itself, with an indicator of what profile created the rule. This means that the details of the rule are available to the server.

When a message arrives, the server compares it with the list of rules. If the server can execute the rule, it does so. If not, it places a deferred action message (DAM) in a hidden Deferred Action folder in the mailbox.

When the user runs Outlook, the client checks the Deferred Action folder and examines each DAM. If the rule was created with the current profile, Outlook carries out the actions indicated in the DAM. This helps explain why rules may fire in an order different from that listed in the Rules Wizard: If the user is not logged in, rules that run on the server execute first, while client-only rules don't fire until the next time the user runs Outlook with the appropriate profile.

Note that if a mailbox is over its size limit, it cannot execute any rules that will send replies or forward items.