Email address marked as spam mule by rooster site

I recently configured sendmail on a fresh Linux server installation and had a configuration issue. I was provided with a link to a website that featured a rooster and asked to consult with them regarding configuration issues.

I can't remember the url of the site, but it seems to be well known.

Can anyone here remind me what a site is and how I was lucky enough to use it to figure out the correct configuration?