Some of the time it depends who your email provider is. Some don't allow marketing emails through, some don't allow attachments. Some will detect marketing emails on keywords alone.

I have 2 email accounts set up. One is a free service, the other is my home ISP's webmail service. The free service will send me an email if there is anything in my spam folder, my paid for webmail service won't.

I had the problem where my webmail inbox kept showing the "Show more" button and it was saying 254/350. To clear it I just left it connected to the server for longer than I usually do, which leads me to believe that part of the problem can be caused your network provider.