Instructions
1) In your Outlook application, click the File tab.
2) Click Manage Rules and Alerts.
3) Next to "Apply changes to this folder", choose the account for which you wish to set up desktop alerts. Then, click New Rule.
4) Under "Start from a blank rule", click Apply rule on messages I receive. Then, click Next.
5) Check the boxes next to "through the specified account" and "on this computer only." At the bottom, under the "Step 2" section, click specified.
6) Choose the same account as the one you chose in Step 3, and click OK.
7) Click Next.
8) Check the box next to "display a Desktop Alert" and click Next.
9) There will be no exceptions needed. Click Next.
10) Type a name to identify this rule, and then click Finish.
11) A pop-up window will appear letting you know that the rule will only run when Outlook is running. Ensure that you understand the message. Then, click OK.
12) To make sure that the alert is being shown for each and every email message that is being received for your selected account, you should place the newly created rule all the way at the top of your other rules for that account. If you do not want new mail desktop alerts to be shown for messages which are being moved to another folder, you will need to sort your "move to folder" rules above this new rule and add the action "stop processing more rules". Click Apply when done.
13) Repeat these steps for the other accounts for which you wish to see desktop alerts. Be sure to specify those accounts in Steps 3 and 5.
Outcome
Your desktop alerts for your chosen accounts will be enabled to display on your Windows PC.