email – Google putting all mail to spam

This question is related to some software for schools and one part is for the schools to send information to students and parents. But all mail end up in Gmail spam folders.
If i look at the google postmaster tools for the last 120 days it says this:

  • User reported spam: 0%
  • Ip Reputation: 100%, but only for one day. No other records
  • Domain reputation: High (on top) but with one day falling down to medium (when the schools starts after holiday)
  • Spam feedback loop: 0%
  • Authenticated traffic: 100% (DKIM success rate, SPF success rate, DMARC success rate)
  • Encrypted traffic: 0% (inbound tls rate)
  • Delivery errors: 0%

Allmost like they just put it to spam because its a competitor to their own products.

(by some strange reason, when the school where my kids go to send a messages, they arrive at my private gmail inbox, but not for other parents)

Is it time to give up on using email and force the receivers to install an app?

I dont know what more to do to prevent the mail from going to spam. Any advice on what to do?

Theoretical question: Does google not like it when the user never visited the page (same domain name as used for the sender email address) and yet receives emails from it? (email etc is collected from schools and registered by them)

These technical requirements are met:

  • SPF setup
  • DMARC setup
  • DKIM setup
  • IP Reverse lookup to sender domain

It is only google sending the mails to spam