This is a screenshot of the manual action email warning that was sent to a publisher.

That publisher is not alone. Others have reported guest post manual actions from Google.

Forensic SEO Alan Bleiweiss (@AlanBleiweiss) tweeted about a client who reported an outbound link penalty. That penalty was also related to guest posts.

And a client just got slapped with an unnatural outbound link penalty. This is the price you pay when you allow “guest posts” without proper due diligence, or without ensuring your site is not exposed to shady tactics.

— Alan Bleiweiss (@AlanBleiweiss) February 15, 2020