plain text

I?m the e-mail administrator. I ran in to a problem some of my remote users who are using outlook 2K to check there e-mail are telling me that when I or anyone else sends them an e-mail if it is rich text it is converted to plan text. I?ve looked and look but can?t seem to find anything that would suggest that there is a setting to convert all rich text messages to plain text. We are running exchange server 5.5 and I check to see if there was a setting in there and there is how ever it is not enabled. If anyone out there can help me I?d be vary grateful. Thanks in advance!