I have a droplet with sentora, the problem I have is that when sending an email this arrives in the spam box (I did the tests of sending mails to gmail and Outlook).
I have configured the DNS of the Digital Ocean ...
There's no reason to have the settings in Sentora also, since you're using DigitalOcean's name servers, so it should be enough to have the configuration there.
Have you set your PTR (reverse DNS)? It shoul...