There are several Google Groups that I subscribe to and this regularly happens:
A real person who I know in real life, whose messages I care about posts to Google Group from a Gmail account, and the message ends up in my own Gmail spam filter.
Like - the message didn't even leave the Google infrastructure and it got tagged as spam?!
I've had email messages from Google about Google products for which I have an active account using my Google email address get marked as spam by Google spam filters.
A real person who I know in real life, whose messages I care about posts to Google Group from a Gmail account, and the message ends up in my own Gmail spam filter.
Like - the message didn't even leave the Google infrastructure and it got tagged as spam?!