How do you handle this ?

Sometimes I get lots of spam email, more so than others. I usually just delete it, but sometimes I will click on the 'unsubscribe' option and sometimes my email address is already filled in. On those I click 'unsubscribe' and it seems to work for awhile.
Also sometimes my email address is NOT filled in. There is a blank with a note like " Please fill in email address " . What ! Why should I do that ? They already have my email address- or do they ?
Now I think this is just a trick to get some real live email addresses. Then they will spread them around and send you more spam.
What do you think and what do you do ?
Just curious.