a lot of the crap spam is because the spammer badly formatted it before it got sent.
then there is the spam which is trying to get a reaction from a recipient telling the spammer to fuck off - that tells the spammer that the e-mail address is live
then there is the spam sent by you to you - that's a sneaky little trick that often gets people to sit up and go wtf?? and gets a reaction from you. the spammer has basically spoofed you and got under your skin.
and it doesn't matter how many defences you put up - some will still get through. the spammers aren't thick and are often ahead of the spam busters with new ideas to get around spam controls.
I don't get a lot of spam but it still fecking annoys me when I do!