That won't help you much, if there's an attachment that automatically runs whenever you read the email. Changing the time it takes OE to mark a message read, has nothing to do with protecting yourself from being infected by a virus that runs whenever an email is opened, or previewed.
If you insist on just opening every email that comes in, regardless of whether or not something might be attached to it, set your mail reader to only render the message in plain text (in OE: Tools > Options > Read tab > Read all messages in plain text ). That will open any emails, but all the text will be just that, text. Any html code that would have been present, has been stripped, and added as an attachment. If you know the email's safe, and would like to view it as intended, you can just open the ATTXXXX.htm attachment.
Of course, while that's generally safe, I still prefer to play on the side of caution, and just open my emails in raw text, when I'm not sure what they're about. All email readers should be able to do this, but I can't say for certain. In OE: Right Click the message > Properties > Details tab > Message Source button. That will open a window with the raw text, all the headers, mime declarations, etc, will be plainly visible, any text will be readable, unless it's spam. If spam, they like the surround ever one or two letters in html comments. It's retarded. A friend sending you email in html form however, will result in you seeing the html code, and the text or body of the html/email will be fully ledgible. Links will not by hyperlinks, you'll have to physically copy and paste them into your browser, if you want to check them out.
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