How does opening an email introduce malware?

Obviously downloading any attachment from a suspicious email is going to spell trouble, but how can malware effect the computer by simply opening the email? Data isn't being stored on the computer, as far as I know, its stored on the clients servers, ie. yahoo, google, etc. The only way I could see it working is if the victim is using a client like Outlook where all the email is saved locally, where the malware is stored on the hard drive and can then execute.|||It's attachments that introduce malware (according to the site below) while viruses can can come from just opening any email. Norton says you can scan the attachment without opening it (how?) and to turn off your preview pane on your email account. (That I've done in Outlook) and to read email in plain text . I guess it's the text format: HTML or Rich Text that carries the virus.|||you have your email contacts--correct ? why do you have to open every piece of mail you get , now you are a target !!! along with fb , twitter , and the rest of the known sites that harbor infections

--you better start reading the serious questions here .. these people are really infected and think nothing of it

you get maleware from your friends and everywhere