A lot depends on what you are using to look at your email. The problem is with email, isn't it? If its just the program that your service provider provided, there might be something in the settings or options. If its something like Thunderbird, it might have adaptive learning that can steer suspected junk into your junk folder. When its not sure, it will warn you and you get the chance to mark it as junk, after which stuff from the same source will be redirected to the junk folder automatically.
