Spambots are non-discriminating - they just send out bunches of the stuff to all computers everywhere!
If you really have a slow day some time you can do this:
1. On your email program, find out how to Display All Headers or View Original Email.
2. Look carefully through all the wee letters and numbers and look for the last "From:".
3. That last From will have an IP address. Copy that and paste into the search box here: https://www.arin.net/ The search box is waay at the top left of the page.
4. If the spam originates in North America it will provide the IP information. Find the "abuse@" address or similar and copy it.
5. Go back to your spam mail and forward it - WITH the original headers etc - to the "abuse" email addy.
Note - the originating IP may be in Asia/Pacific (APNIC), Europe (RIPE) or other databases. ARIN will provide the link to those if needed.
I did this years ago before Spam filters were at all common.
"Remember that children, marriages, and flower gardens reflect the kind of care they get." -- H. Jackson Brown, Jr.