Tom, it depends on what you use to view your emails and which email you get
Some email clients open the emails in memory when you click on them to delete, some don't, some even do this with the attachments.
The other thing is if this is available in a text attatchment it is also possible to be contained within the email itself and now that the virus is out there, expect some people to mutate it and release it again.
In the old days if you didn't open the mail and just deleted it you would be safe, not the case these days I am afraid, the only way to be safe is to have the best Anti Virus and update it frequently. Also to ensure you do a full check often, sometimes a virus can sneak through your resident shield but be found by a full scan.
In the pdf I have comparing the top Anti Virus softwares they threw some common nasty things at them and quite a few of them didn't notice so having the software doesn't mean you can relax either

gets worse doesn't it?
The best advice I can give is update often, check often and if you click on an email and without opening it the mail is shown in a window as a preview, turn that "feature" off.
Some clients allow you to only get emails from people you know, that is you create a list of allowable senders and only those mails are downloaded to your pc, that is also a good idea but impractical for some.
Anyway, I wish I could give us all some advice to enable security but sadly the boat already has many holes in it, it is just which holes we stick our fingers in and which we don't.
BaB
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