It looks like you can't view the mail that is received by your mail service before they send it to you and they also forward everything that they get. This would not be something I would want.
As someone stated above, a service like St Brendan's Isle (which I have) will give you the option to view on-line the front side of every piece of mail that is received. You then choose what you want forwarded and what gets shredded by them. I can also set up my mail so all 3rd class junk mail is automatically trashed.
I would advise you to change to a different service if you can't at least view your mail online. I know this would be a major pain and I wouldn't want to do it either.
Last - Which service do you use ?
Tim