Outlook Rules Guide: Create Them and Stay Under 256 KB

A rule is a name, a condition and an action

Microsoft's rules page says every rule needs a name, a condition and an action, and exceptions are optional. Rules run on incoming mail and can change importance, move messages to folders or delete them. They run in the order they appear in the list, and a toggle beside each rule pauses it without deleting it.

New Outlook: right-click, then Rules

In new Outlook for Windows, right-click a message, point to Rules and choose Create rule. Pick a folder and press OK. The rule then applies to every future message from that sender or those senders. For several conditions or exceptions, choose More options instead.

To change a rule later, go to Settings, then Mail, then Rules, open the More actions menu (three dots) and choose Edit rule. Use the Up or Down arrow to change the order. The Run rule now icon beside a rule applies it to messages that are already in your mailbox.

Tick "Stop processing more rules" when a rule should be the last one to touch a message. A good first rule has 3 parts: from news@example.com (condition), move to the Newsletters folder (action), and stop processing (so rule 2 and later never see it).

Classic Outlook has the Run Rules Now window

In classic Outlook, right-click a message, choose Rules, then Create Rule. Tick "Run this new rule now on messages already in the current folder" to apply it to old mail. The longer route is File, then Manage Rules & Alerts, then New Rule, where you can start from a template.

Run Rules Now in the same window lets you choose which rules to run, a folder (with or without subfolders) and whether to apply them to all messages, read ones or unread ones. A broken rule shows in red in Manage Rules & Alerts: select it and edit the underlined links in the rule description.

Outlook on the web and Outlook.com differ on old mail

On the web with a work or school account, go to Settings, Mail, Rules, then Add new rule. "Stop processing more rules" is on by default there, so only the first matching rule applies. The page lists no run-now option for existing messages, and it treats Outlook.com and work or school accounts as 2 separate cases.

Outlook.com with a personal account is stricter: rules cannot run on existing messages in the beta and apply only to new mail. Microsoft points to Archive, Move to and Sweep for tidying what is already there. Outlook.com also warns that rules made in other Outlook versions may not run or be editable there.

The 256 KB limit counts size, not the number of rules

Inbox rules in Outlook on the web and the desktop apps share 256 KB in total on Exchange Online. Microsoft says there is no maximum number of rules, because size is what counts: a long rule name or many conditions take more space. When you reach 256 KB, you are warned that you cannot create or update rules.

Only enabled rules count. A mailbox can hold any number of disabled rules, so switch off seasonal rules instead of deleting them. An administrator can lower the quota to a value from 32 KB to 256 KB, for example with Set-Mailbox and -RulesQuota "200 KB", but nobody can raise it above 256 KB.

If a mailbox was migrated, its limit might sit below the 256 KB Exchange Online default and can be raised by an admin. Older mailboxes explain why: on Exchange 2007 to 2013 the default was 64 KB, customizable up to 256 KB, and Exchange 2003 allowed 32 KB. Microsoft's older troubleshooting page lists 5 ways to shrink rules: shorten names, delete old rules, combine similar ones, move a .pst file to a short path, and clear "on this machine only" for rules that move mail to a .pst file.

A worked example: 45 colleagues in one client-only rule

You want classic Outlook to play a sound for mail from 45 people picked from the Global Address List. Playing a sound, assigning a category, flagging, printing, marking as read, permanently deleting and showing a desktop alert all turn a rule into a client-only rule.

Microsoft documents that a client-only rule with 20 or more GAL people fails, while a rule with 2 people works. You see "One or more rules cannot be uploaded to Microsoft Exchange and have been deactivated". The fix is 19 or fewer people per rule, so 45 people need 3 rules (19 + 19 + 7), or one distribution group added to a single rule.

Client-only rules need Outlook open on that computer

Most rules run on the server and work with Outlook closed. Some run only while Outlook is open, and classic Outlook shows a warning when you create one. Custom action rules depend on third-party add-in DLL files that must be installed on that computer, and they run only there.

Rules from classic Outlook may not work in new Outlook if they are client-side. Microsoft's advice is to create a new rule to replace the migrated one.

Gmail, Yahoo and iCloud accounts need rules at the provider

New Outlook does not support rules for third-party accounts such as Gmail, Yahoo and iCloud. Set up those rules with the email provider. This is the first thing to check if the Rules menu does nothing for a non-Microsoft address.

Forwarding, redirecting and other mistakes

A forwarded message shows as forwarded and replies go to the forwarding address. A redirected message keeps the original sender, so replies go to that person. Pick the one that matches what you want.

A forwarding rule can take more than one address, but the number may be limited by your account settings, and a rule with more addresses than allowed will not work, so test it. Exchange also lets a message be redirected only 1 time by inbox rules, so a chain from you to a colleague to a third person stops after the first hop. Company-wide transport rules are a separate system, limited to 300 rules of 8 KB each, and an admin manages them, not you.

If an Outlook rules error is on your screen and the wording is unclear, Crade can read it and explain it.

Who should use rules and who should not

Rules suit steady patterns: newsletters, receipts, a boss's messages, a project mailing list. They suit people on Microsoft 365 or Outlook.com. They are a poor fit for one-off cleanups of old mail on Outlook.com, where Sweep works on existing messages, and for Gmail or Yahoo accounts in new Outlook, where the provider's filters do the job.