some users complained about corrupt pdf files sent using squirrelmail. i noticed in most cases enconding was wrong, it was text/download, sending a lot of binary code and different newline breaks from the original causing the corruption.
this only happens in some computers with firefox, i was able to correct it in a computer after reading http://techblog.procurios.nl/k/618/news/view/15872/14863/Mimetype-corruption-in-Firefox.html
basically editing mimeTypes.rdf and deleting all wrong pdf entries, leaving only application/pdf
this is just in case someone had the same problem.