Automatic conversion of incoming message to .eml attachment

When I open an incoming mail, the message briefly shows up on my OE6 window

for less than a second, and then the message automatically converts to an

attachment with .eml file form. I have to read the message on internet

explorer window by opening the .eml file. This situation occurrs only from

one particular person, not all other person. Is this my e-mail option

setting problem or sender's option problem? M.hahn