|There are many reasons why a specific user's emails wouldn't reach you. Did you check if their mail ended up in your Junk or Deleted mail folder?|
1. Make sure that the user has the right address in their address book for you, and that the company's address book is correct and up to date.
2. Check your blocked senders list, in the Junk E-mail options dialog, to see if you have accidentally blocked this user.
3. Add this user to your safe senders list in the same dialog box. While you're at it, add the whole company address book in your safe senders list.
4. Make sure your junk e-mail protection level is not set to "Safe Lists Only". Try setting it to a weaker level of protection.
5. Open the Rules and Alerts dialog and make sure there is no rule for sorting this sender's messages somewhere you wouldn't find them.