I have a perfect score in google postmaster tools on dkim, spf and 0 spam reports. They still send all emails to spam. They will even do this if you are replying to the user who contacted you. Same experience for my friend running an indie festival. These days you pretty much have to alert gmail users by some other means (like if signing up on a website) that they have to check spam and whitelist you since it appears gmail would rather block legit emails than allow a single possible spam through.