Client-Only Rules vs Server-Side Rules in Outlook

"Client-only" on an Outlook rule means the rule contains at least one condition, action or exception that only the classic Outlook desktop app can perform, so it runs only while classic Outlook is open on the computer that created it. A server-side rule uses only steps the Exchange mailbox can handle by itself, so it runs whether or not any device is switched on.

Outlook decides which kind a rule is from what the rule contains, not from what you meant. You don't pick "client" or "server" anywhere in the Rules Wizard. Add one Outlook-only step to an ordinary filing rule and the whole rule becomes client-only.

This guide covers the exact conditions and actions that cause it (from Microsoft's own list), how the label behaves in classic Outlook, new Outlook, Outlook on the web and Outlook for Mac as of October 2026, and how to turn a client-only rule back into a server-side one.

Client-only vs server-side Outlook rules at a glance#

Both kinds are built in the same Rules Wizard and look the same in the list. The difference is where the rule executes, and that decides whether it survives a closed laptop, a second device, or a move to new Outlook.

How to tell if an Outlook rule is client-only#

Classic Outlook tells you in three places, so you rarely need to guess.

• The rule list. Go to File > Manage Rules & Alerts. A client-only rule shows "(client-only)" after its name.
• The warning when you save. Finishing a rule that needs Outlook brings up a message saying the rule is client-only and will only process while Outlook is running.
• "On this computer only". If the rule depends on something that exists on one machine, such as a folder inside a PST file, Outlook adds this condition automatically. On your other computers the same rule appears marked "(for other computer)" and does nothing there.

Which conditions and actions make a rule client-only#

Microsoft's support article on fixing broken rules lists common examples. The lists include some items people expect to run on the server, such as "mark it as read" and "assigned to category". That is why a plain-looking rule can still come back client-only.

The table combines Microsoft's examples with the local-file actions that always need the desktop app, then shows what to use instead if you want the rule to run on the server.

POP and IMAP accounts: every rule is client-only#

One account type skips the whole question. POP and IMAP accounts in classic Outlook have no Exchange mailbox behind them, so there is no server-side rule engine to hand the rule to. Even a plain "move to folder" rule on a Gmail or Yahoo account added by IMAP needs classic Outlook open.

New Outlook goes further: its rules work only on Microsoft-hosted mailboxes, so a POP or IMAP account there gets no Outlook rules at all. For those accounts, use the provider's own filters (Gmail filters, for example), which run on that provider's servers.

To check the account type in classic Outlook, go to File > Account Settings > Account Settings. The Type column shows Exchange, IMAP/SMTP or POP/SMTP.

Which Outlook apps support client-only rules (October 2026)#

Only one app can create client-only rules. Microsoft's own pages are the source for each row. Check them again if you read this much later, since the newer apps are still gaining rule features.

How to change a client-only rule to server-side in Outlook 365#

Outlook has no "convert to server" switch. You get a server-side rule by removing every Outlook-only step, and the most reliable way to do that is to rebuild the rule somewhere that can only make server-side rules.

1. 1

   List your client-only rules

   In classic Outlook, open File > Manage Rules & Alerts and note each rule marked "(client-only)", plus its conditions and actions. Take a screenshot; you'll rebuild from it.

2. 2

   Find the line that trips it

   Compare each step against the table above. It is usually one line: a sound, an alert, a PST destination, a category, a flag, or "mark as read".

3. 3

   Rebuild it in Outlook on the web or new Outlook

   Go to Settings > Mail > Rules and create the rule again. Every rule saved there is server-side. Steps like "Mark as read" and "Categorize" are available there and run on the server.

4. 4

   Or edit in classic Outlook, then recheck the label

   Replace the offending step (a mailbox folder instead of a PST folder, Delete instead of Permanently delete). If "(client-only)" or "on this computer only" stays, delete the rule and rebuild it.

5. 5

   Turn off the old copy

   Once the server-side version works, disable or delete the classic client-only rule so the two don't both act on the same messages.

6. 6

   Test with Outlook closed

   Quit classic Outlook on every PC, send a matching message from another account, then check from your phone or the web. If it's already filed, the rule is running on the server.

When you genuinely need a client-only action#

Some jobs only the desktop can do: a sound for one VIP sender, a printed copy, a local script. You can keep those without letting the important part depend on your PC.

• Split the rule. Put the filing (move, categorize, forward) in a server-side rule and keep only the sound or alert in a client-only one. Test it: if the server rule moves the message out of the Inbox first, the client rule may never see it.
• Catch up with Run Rules Now. Client-only rules don't fire retroactively for mail that arrived while Outlook was closed. In Manage Rules & Alerts, Run Rules Now applies a rule to a folder you choose.
• Keep classic Outlook running on the PC that owns the rule. That is the only way a client-only rule stays current, and it stops the moment that machine sleeps.

Server-side rule limits in Exchange Online#

Server-side rules share one storage quota per mailbox. Microsoft's Exchange Online limits page lists the inbox rule limit as 256 KB on every Microsoft 365 business and enterprise plan. A mailbox migrated from on-premises Exchange may carry a lower limit that an admin can raise.

In practice, long lists of sender addresses or keywords use up that space fastest. If Outlook refuses to save a new rule, merge rules that share an action before you delete anything.

Server-side rules come with any Exchange Online, Microsoft 365 or Outlook.com mailbox. There is no add-on to buy. The account type decides whether you get them, not the plan.

Which kind of rule to use#

• Use server-side if you read mail on a phone or more than one computer, want rules to keep working while you're away, or plan to move to new Outlook. That covers most people.
• Keep a client-only rule only for an action that has to happen on your machine, or when the account is POP/IMAP in classic Outlook and has no server-side option.
• Use neither for company-wide policy. Routing every invoice to accounting no matter who receives it belongs in a transport (mail flow) rule set by an admin in the Exchange admin center. That runs before mail reaches any mailbox.

If you're tired of rebuilding rules#

Converting a client-only rule fixes where it runs, but it is still a list of fixed conditions you maintain by hand. When a sender changes domains or a client starts writing from a new address, you edit the rule again.

AI Emaily's inbox rules run in the cloud as mail arrives across Gmail, Outlook and IMAP accounts, so they behave the same whether your laptop is open or shut. They can match on sender, subject, keywords and attachments, or on a concept you describe in plain English, then label, archive, star or quarantine the message. We build AI Emaily.

It doesn't replace the one thing classic Outlook does that no cloud service can: play a sound on your PC, print, or launch a local script. If that's the job, keep the client-only rule. Org-wide routing still belongs in an admin's transport rules.