I use MS Exchange and was having problems on another list server and traced the problem to MS Exchange's Rich Text Format (RTF) feature. It was suggested to me also that I switch to Eudora, but I was able to discover the trick for turning the RTF feature off, and things have been fine since then. Perhaps your problem is due to the same cause. Below is my current understanding of the solution.
The option for turning RTF on or off is present as a property of entries in the address book. Thus three things are required in order to prevent RTF from being invoked when sending a message: 1) the recipients of the message have to be listed in the address book, 2) their entries in the address book must have RTF turned off, and 3) the message has to be addressed to them via the display name of their entry in the address book rather than by their email address.
The third requirement is a little confusing. By way of example, in my address book, I have an entry for you with display name "Peter Phillips", email address "p.m.phillips@cliff.shef.ac.uk", and the RTF feature turned off. When I send you a message, I have the choice of filling in theTo field with "Peter Phillips" or with "p.m.phillips@cliff.shef.ac.uk". If I fill it in with "Peter Phillips", then the message will go out with the RTF feature turned off. If I fill it in with "p.m.phillips@cliff.shef.ac.uk", then the message will go out with the RTF feature turned on. In MS Exchange parlance, "p.m.phillips@cliff.shef.ac.uk" is referred to as a one-off address, and MS Exchange apparently does not look for these literal addresses in the address book. Address book entries are matched only by display name. With a one-off address, then, MS Exchange does not get the RTF information out of the address book and thus turns the RTF feature on by default.
This issue is a little trickier when replying to a message. If the sender of the original message uses a different display name than what you use for them in your address book, then the reply address that is