Hi @Small Guang
Welcome to our forum!
Do you mean how many rules can be created in Outlook?
As far as I know, there is no limit on the number of mail rules in Outlook. Outlook desktop apps are limited to 256 KB total for all rules. Each rule you create will take up space in your mailbox. The actual amount of space a rule uses depends on several factors, such as how long the name is and how many conditions you've applied. When you reach the 256 KB limit, you'll be warned that you can't create any more rules or that you can't update a rule. More information, see: Modify the space used by Inbox rules in Exchange Online | Microsoft Learn.
Having over 100 rules is not very manageable though. Consider using other sorting methods such as custom views, Search Folders and simply using Instant Search to get what you need. More information, see: Managing a large amount of message rules - MSOutlook.info.
(Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
Hope this helps!
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