e-mails sent from our WooCommerce Store to recepients using gmail are spammed

Job ID: 33398010

Budget: $50 – $100 USD

We have a Wordpress based WooCommerce store.
We try to send e-mail from this store to our clients from <xyz>@<ourdomain>.<ch> but e-mails sent to gmail addresses are spammed by Google.
We tried a lot of things: Google domain verification, Valid DKIM, SPF, PTR, WP mail smtp plugin and external sendinblue.com smtp provider, no success yet, e-mails are still spammed. :-(
If you are expert and you can solve our issue, we say thank you and pay the bill.
If you DON'T solve the issue, we WILL NOT pay the bill.
We need someone have the real experience and solution for this issue!