A user had mismatched rules in Outlook and his Exchange mailbox and wasn't sure what to do.

When I edit my rules, Outlook always asked if I want to use the Client or Server rules. What is the difference between them? Which should I be using?

Outlook stores rules in the Exchange server mailbox (including Outlook.com accounts) and syncs a copy of the rules to Outlook on your desktop. This message comes up when Outlook detects the rules on the server are not identical to the rules stored in the Outlook data file and Outlook needs to know which ones you want to work with. If you know one set is correct, choose it, otherwise choose Server.

To eliminate the message, you can start Outlook with one of the cleanrules switches:

If you clear only the client rules, the server rules will sync down to Outlook; clearing the server rules works the same way, with the rules stored in Outlook syncing up to the server.

You'll first want to export the rules. This will allow you to restore the rules quickly and provides insurance, should something go wrong and you decide to delete all of the rules.

1. Open the Rules & Alerts dialog, click Options and then Export rules.
   
2. Close the Rules & Alerts dialog then close Outlook.
3. Press Windows key + R on your keyboard to open the Run command.
4. Type or paste outlook.exe /cleanrules in the Open field to clear all rules.
   Use outlook.exe /cleanserverrules if you know some client rules didn't sync up to the server.
   Use outlook.exe /cleanclientrules to keep the server rules.
   
5. Press Ok to restart Outlook.

If you used the /cleanrules switch, import the rules you backed up earlier. If you used either the client or server switch, open the Rules & Alerts dialog and choose which rules to keep one last time. The rules will sync so both client and server are identical.