Attached DOS text files being converted to Unix text format

[Damián Rodrí­guez Sánchez]

I've already sent this to a Mozilla Thunderbird list but received no 
answer yet.

All e-mails I receive containing DOS text files are being converted to 
Unix text files when I save them. Unix text files are not changed. Other 
file formats are also not affected (zip, exe, doc, etc). I'm not sure if 
this is a Thunderbird problem. I'm running Thunderbird on FC9. Any help 
will be appreciated.