Mail attachments: loss or change of format, file name and extension?

Hello! I am using Apple Mail 2.1.1. and have a very annoying problem with sending mail attachments. On the way to the recipient the file format, file name and extension is changed or completely lost. A word-document that had a proper file name before is received as "noname" without an extension and format. pdf-files also lose their file extension, the file name is cut, but it can still be detected as a pdf. Still it is very unprofessional to send mails like this. I cannot understand the problem espacially since it does not change the problem if I chose "send attachments windows-compatible" or not. Maybe someone can help me?
Thanks a lot! Best regards from Berlin, Maximilian Kall