The other day I had to sign a NDA from Google and it ended up in the spam folder. We were on the phone for over 20 minutes just waiting for the NDA to come, until I decided to check the spam folder and sure enough, there it was.
The spam filter is in my opinion too dumb for this age. Once you mark one email from one domain as a spam, every single email from that domain ends up in the spam folder also. For instance I don't want to see stupid Comcast commercial offerings but I need to receive my invoice every month. Unsubscribe works sometimes, but not all the time.