August 2026 · Henry Bravo

Client-Only vs Server-Side Outlook Rules: Which Ones Do You Have?

If your rules fire when you are at your desk and not overnight, on your phone, or in Outlook on the web, nothing is broken — they are client-only rules. This explains how to tell which of yours are which, and what to do about it.

A server-side rule is stored in your mailbox and runs on the Exchange server whether Outlook is open or not, so it applies on your phone and in Outlook on the web as well. A client-only rule runs only while Outlook is running on the specific computer that holds it. Outlook decides which is which automatically: a rule becomes client-only the moment it uses a condition or action the server cannot perform — playing a sound, showing a Desktop Alert, printing, running a script, starting an application, or moving mail into a local .pst file. Outlook labels these (client-only) in Manage Rules & Alerts, and that label is the fastest way to answer the question for your own mailbox.

The Difference in One Paragraph

Your rules live in one of two places. Server-side rules are stored in your mailbox on Exchange and executed by the server as mail arrives — they work at 3am with every device switched off, and their effects are already there when you open Outlook on your phone. Client-only rules are executed by the Outlook application on your computer, so they only run when that application is open, on that machine.

You do not choose between them. Outlook makes the decision for you, based on whether the server is capable of doing what the rule asks.

How to Tell Which of Yours Are Which

In classic Outlook, go to File → Manage Rules & Alerts. Look at the rule names. Any rule the server cannot run has (client-only) appended to it, automatically. Nothing else needs checking — if the label is absent, the rule is server-side.

It is worth doing this once even if nothing appears broken, because the label explains a surprising amount of behaviour people otherwise attribute to bugs: mail that is filed by the time you reach your desk on some days and not others, folders that look different on your phone, rules that seem to skip messages.

What Forces a Rule Client-Side

Any one of these is enough. It is not cumulative — a single unsupported action makes the entire rule client-only, even if everything else in it is ordinary:

Play a sound
Display a Desktop Alert or a message in the New Item Alert window
Print the message
Run a script
Start an application
Move or copy into a .pst file — a local data file rather than a mailbox folder
“On this machine only” ticked in the rule’s settings

The .pst one catches most people. Filing into an archive that lives on your hard disk feels like ordinary filing, but the server has no access to your hard disk, so the rule cannot run there.

Why It Matters More Than It Used To

When everyone used one desktop PC that was on all day, a client-only rule was nearly indistinguishable from a server-side one. That is no longer the case:

Mail read on a phone has not been through your client-only rules at all.
Outlook on the web shows an unfiled inbox, because the rules never ran there.
Anything arriving while your machine is off is processed in a burst when you next open Outlook, which is why a morning inbox sometimes reorganises itself in front of you.
Two computers running the same client-only rules against local files will conflict, and Outlook may deactivate rules as a result — one of the three causes covered in why Outlook rules keep turning off.

The New Outlook Wrinkle

The new Outlook for Windows runs server-side rules only, and supports a narrower set of conditions than classic Outlook. Client-only rules do not migrate. If you have moved and found rules missing, this is usually why — they were not lost, they were never portable.

What you can do: rebuild them as server-side rules where the actions allow it, or keep them in classic Outlook, or apply them by hand with Run rules now.

Converting a Client-Only Rule

Usually straightforward, and usually one of two changes:

File into a mailbox folder instead of a .pst. Create the destination inside your mailbox rather than in a local data file. The rule immediately becomes eligible to run server-side.
Clear “on this machine only” in Change Rule → Edit Rule Settings, unless you genuinely want the rule confined to one computer.

Then drop the cosmetic actions. A Desktop Alert or a sound is almost never worth making a filing rule dependent on the application being open — and if you want the alert, it is better set up separately from the rule that files the mail.

When You Cannot Convert It

Some rules are client-only because they genuinely need a client: running a script, launching an application, printing. Those cannot be made server-side at all, and the honest answer is that they will only ever run while Outlook is open. If the point of the rule was to file mail reliably, it needs to be split — a server-side rule to do the filing, and a separate client-only one for whatever else it was doing.

If the reason you are reading this is that filing does not happen reliably, Folder Suggest takes a different approach: it reads each email in front of you and suggests the right folder from your existing structure, one click to file. No rules, no client-versus-server distinction, and the AI runs on your own device.

Add to Outlook

Frequently Asked Questions

How can I tell if an Outlook rule is client-only?
Open File > Manage Rules & Alerts. Any rule Outlook cannot run on the server has the text (client-only) appended to its name in the list. There is no separate setting to inspect; the label is applied automatically based on what the rule does.

Why do my Outlook rules only work when Outlook is open?
Because they are client-only. Server-side rules run inside Exchange and do not care whether Outlook is running, but a client-only rule is executed by the Outlook application itself, so it can only fire while that application is open on that machine. Mail arriving overnight is processed when you next start Outlook, not as it arrives.

What makes a rule client-only?
Any condition or action the Exchange server cannot carry out. In practice that means: play a sound, display a Desktop Alert, print, run a script, start an application, mark as read on some versions, move or copy into a local .pst file, or having 'on this machine only' ticked. One such action is enough to make the whole rule client-only.

Do client-only rules work in the new Outlook for Windows?
No. New Outlook runs server-side rules only and supports a narrower set of conditions than classic Outlook, so client-only rules do not carry over when you switch. They have to be rebuilt as server-side rules where that is possible, or run manually with Run rules now where it is not.