I’ve installed a HestiaCP. All forwarded mails were going to the Spam folder of Gmail accounts. When I checked the my server IP, it was under UCEPROTECTL3. As far as I read, getting off this list is also a difficult process.
Hestia also has the ability to send mail via SMTP and is active for some domains. I wonder how it would be if there was an option to send over SMTP while forwarding mails? or is there any option like this?