Yes 10/10you have 10/10 on mailtester?
Where do you check gmail log? Thanks.check log from own gmail account why it was marked as spam in your case.
I checked the IP and they are all green, no bad ones.also check IP in blacklists.
This is already set long time ago. Also the spf and dkim. Thanks.The reverse dns should match the hostname of your server and the hostname should forward to the ip address. Make sure you have spf set up as well as dkim.
DMARC certainly can help, but probably if there are other issues, maybe bad reputation or previous listings of the ip address.DMARC should be also there , rescued many customers from Google blacklist with that.