that the email addresses they use are not their own. It may be someone else's, it may be an non-existing email address, they don't care.

Most webservers have a SPAM filter of some type. Use the Spam filter on the webserver first. I found out with the email provider I use(Gmail), I get very little SPAM messages that slip into my inbox. I then go to the webserver and tell it that it's SPAM and never see it again.

There are other programs out there that also help.

If using an email program you can read the headers by:

Opening the email

click on view

click on message source