Google began sending mails from my server to SPAM folder

[fmc000]

Perhaps you trained the filter by sending to spam some old mails from google?

No, I actually found their spam filter to be pretty accurate. I don't recall having done anything like that.

 

[aragats]

Does it also forward the spam?

It used to have such option, and I used it. At some point I noticed it doesn't forward spam anymore.
One suggests creating a filter for that, I haven't tried though.