File extensions change in mail

[Mbenzi]

I have a Mac, in a Mac-hostile PC environment. We work with customers and compatibility is very important. I therefore had to work hard to get allowed to use a Mac.

It is a MacBook Pro, 2,16 GHz Intel Core 2 Duo, with 3 GB memory.
I use OSX Leopard 10.5.2, when I have to use AutoCad I run that on Win XP through Parallel.

In Mail, I have checked the "Windows compatible" box. I also use visible file extensions.

But what happens, is that my attachments change the file extension name when I send it. This happens with MS Office files, and pdf:s.

Strange enough, it seems to happen with some receivers only.

If I send a Word document, e.g. with the name "Environment.doc", the receiver may get something called "Environment.dococ" and cannot open it (unless first correcting the extension). If I send it as a pdf document with the name "Environment.pdf" it may have the name "Environment.pdf0" when it arrives.

It appears to happen at random, and especially with some adressees or receivers. Unfortunately the owner of the company is one of those, and he has now suggested to scrap my Mac and give me a PC, "because the Mac isn't good enough".

What is the reason for this, and what can I do to correct it?

[VirtualTracy]

I have never heard of this happening before and I can't guess why the extension is changing ... have you tried another email client such as Mozilla Thunderbird as an interim measure while you wait for another answer here and also as another means to narrow down the culprit/s?