Our company is using a Dell server with MS Exchange Server 5.5 on a Windows NT 4.0 platform to handle both internal and external email. We are using Outlook 2000 Exchange Server 5.5 service pack 3 as our email package. Our system is made up of both PC and MAC computers. On the PC side our users have no problems sending external mail with either text or graphics file attachments. The PC users are connected through a switch to the Exchange server. The MAC users are connected to an HP Server running the Windows 2000 Server platform in the Art Dept using TCP/IP. The Art Dept HP Server is connected to the PC network with a fiber connection to the switch. MAC users are having trouble sending attachments. The MAC users can send both internal and external plain emails without any attachments. MAC users can send an external email with a text attachment without problems, but Outlook locks up when they try to send a graphics attachment. We are unable to find any information on troubleshooting this problem.