MS Outlook hanging on receiving E-Mail

I recently replaced a PC in one of our Offices. Everything works fine except Outlook. Outlook syncs with our MS Exchange Server and downloads all of the users E-Mail, but when it comes to sending E-Mail, it constantly looses the connection, then gets it back. The E-Mail may eventually go through but most times will not. All other PC’s in the office are fine, just this one. I did put an IP Address in the Hosts File (along with the Server Name) but still the same problem