Ari Nahmani posted on Facebook (public URL) a message he got for one of his clients in Google Search Console that is unique. It is directly from John Mueller, the same John Mueller we cover here, about a critical and urgent issue with their web site.
The email first explains who John is, then says how the site has issues with search engines. It talks about how URLs are bing returned with a 400 error, preventing Google and other search engines from crawling it. It appears the site has something in place to block Google and other search engines from crawling and Google wanted to let this site owner know.
Here is a copy of the notification in Google Search Console provided by Ari (click to enlarge it):
So here you have it, we always knew Google sent personal messages every now and then - but here is a screen shot of one.
Forum discussion at Facebook.