I have found a text processing bug in Outlook and I would really like to see if it can get fixed in a future version of Outlook. The issue is that if somebody sends a text file that has some other extension Outlook and the sent attachment uses Windows style line endings (\r\n) Outlook will strip the \n out of the document but leave the \r behind leaving the text attachment not conforming to any standard at all.
I have reported this several times to the "Help" people from within Outlook but I don't think they are setup to deal with the level of bug reporting. I have reproducible cases with the files downloaded through the GMail web interface and through Outlook. Thunderbird and Postbox (which is based on Thunderbird) don't have this problem.