i suggest any emails you receive from a sender you dont know, do not even waste your time opening them, just delete them. Thats how many people get infected with a virus if it contains a virus with attachment.
if you want to reduce the ammount of spam you recieve in your inbox downloaded to your computer read and delete your email online if your isp provides this service dont download it to your computer or use something like mailwasher (halfway down page) click here
install it and set up a friends list and use it for a week or two and blacklist any spam you get then set it to delete blacklisted messages and the ammount of spam you get should be greatly reduced. you can safely read mail using this without ever downloading on to your computer.