'Create a maildir message for a user.
@type user: L{bytes}
@param user: A username.
@rtype: L{MaildirMessage}
@return: A message receiver for this user.'

def startMessage(self, user):

    if isinstance(user, str):
        (name, domain) = user.split('@', 1)
    else:
        (name, domain) = (user.dest.local, user.dest.domain)
    dir = self.userDirectory(name)
    fname = _generateMaildirName()
    filename = os.path.join(dir, 'tmp', fname)
    fp = open(filename, 'w')
    return MaildirMessage(('%s@%s' % (name, domain)), fp, filename, os.path.join(dir, 'new', fname))
