this is a little lengthy but should solve your problem, my wife had similar problem and this stopped it.
1. log into My Verizon to view your account. (there should be link at the top of this screen)
2. click on the red (my services tab)
3. on the left hand side there should be a (verizon safe guards) link click on this
4. click on (spam controls)
5. that should show you a screen to block messages. In your case it is internet based so click on (internet spam blocking)
6. The next screen should have 5 boxes that you can type domain names into. I would suggest to type just one domain in each box. (exp box 1 (zmail.com) box 2(ozmail.com)) If you type in the domain it should block all emails from those sites.
Hope this helps