Very good question and, by coincidence, a colleague from IBM Japan, Yasuhiro Onoda, solved this just last week.
    Here is the response from Yasuhiro:
    But I found mail from --file-body does not work well if a file contains multi byte characters.
    (In my cases, I need to write a mail in Japanese. )
    
    I checked the Mail.py file.
    
    These lines are used to read a file.
    -----------------------
       f=open(bodyFile)
       bodyLines=f.readlines()
    -----------------------
    
    But the readlines method of Jython does not work well to read multi byte characters.
    
    So I replaced the above lines with the following.
    -----------------------
        f= BufferedReader(InputStreamReader(FileInputStream(bodyFile)))
        bodyLines=[]
        line = f.readLine()
        while(line != None):
          bodyLines.append(line  + "\n")
          line = f.readLine()
    -----------------------
    
    I also added some classes to this line,
    -----------------------
    from java.io import File,FileInputStream,InputStreamReader,BufferedReader # for multi-byte capable
    -----------------------
    
    It may be dirty, but works fine for my Japanese mails,
     
    So you can get Japanese mails working.
    I included the change in the upcoming 4.2.1 release. The new version is in the release process and will be released as soon as it's approved.
     
    -Sami Salkosuo