How does one actually do this?

I also would like to know this. The theme league invites are insane right now

If you scroll to the bottom of your in-box page you'll see the blue button options to BLOCK or DELETE messages. To block, just check the box next to the sitemail of the person you want blocked, then click on BLOCK.

I think there's a way though to opt out of receiving theme league invites. That seems like a better way to go. I use the block option for truly obnoxious owners, not owners who are just taking advantage of a feature the site offers to promote theme leagues.

Maybe this will do the trick, as far as not getting theme league invites. Go to your account info page, then click on baseball. There are several questions there, including if you're interested in draft leagues, live leagues, and gimmick (theme) leagues. Make sure all of them are checked NO.

I just changed all mine to NO. Let's see if I keep getting invites. I've never received hockey, basketball or football invites so I imagine this will work.

Thanks Stengel. I don't mind one-off theme league invites, but I had one owner spam me repeatedly yesterday with invites for the same league. I mainly just want to block that clown.

I’ve been had all my stuff set to “NO” but I still get all the invites from tab’s career league, or that one dude’s Coors homerun only league. It’s annoying at times.

I would guess those owners have their own list of people they're sitemailing, as opposed to using the site's auto-sitemailing option you see when creating a new theme league. You could respond to their sitemail and ask to be removed from their list. If they refuse, block them.

There's a few from the public list who've asked me to not send invites. Simple enough. I try to get the word out without being annoying.

Yes, if you go to your account settings you can streamline how you receive/don't receive invites. You can also turn on or off receiving emails when sitemails are sent to you.