I'm talking about going to your email webmail site. Like go to gmail, or your IP webmail and mark it as spam. Whatever email program it's coming into.
Here's a partial picture of Google mail's Inbox. Click the box next to the offending email so it has an X in it, then click the Spam button. You won't get it in your Inbox anymore.

I have Thunderbird email and I have my webmail accounts coming into Thunderbird: gmail, Hotmail, Yahoo mail, but marking them as spam doesn't stop them from going to those webmail accounts. They need to be stopped at the source, in the webmail account directly. I occasionally get a spam email in my IP (Frontier.com) email, but I still have to go to the Frontier webmail account to stop them entirely. Frontier knocks them out there.
When I mark them as junk in my Thunderbird account, that doesn't tell the webmail account that it is spam. I like to get them where they are coming in.