Best idea:
1- Only open emails that are from known people or organisations you have dealings with.

2- Tell all friends or affiliates provided with your email details to type who they are, and reasons for the email in the subject bar at least for the initial email.

3- Have your email junk filter set to high, this will put every email from a "non-safe-list" or "unknown" address into the junk (or if you're lucky, a "unknown" folder) area automatically.
This way, while logged into your email, simply cruise through the junk area, delete anything thats not cleared by what I explained in 2, and add those you want to keep to the "safe" or "friends" list. Don't bother "blocking" any of the ads, as they tend to use throwaway email accounts anyway.