how to identify which email contains a virus, ect.?

I still run outlook express on my old windows XP computer, this has the  facility to 'block' email senders.

I receive many emails that contain 'threats' which are blocked and removed by Norton.

how can  I identify these emails which contain malicious content, so that I can add the sender to my 'blocked' listing, rather than simply deleting them and leaving the computer open to further attempts  ?