Set up domain mail so that letters do not fall into spam?

Question

SPF

I'm struggling with getting emails from our mailing list into spam. All domain mail works through the free G Suite (Google).
However, the mailing is carried out from the WordPress site from the plugin: Mailster (that is, in fact, sending from the VDS server via PHPMailer), because G Suite has a limit of 500 emails per day, and we have large mailing lists!
Configured SPF, DKIM and DMARC. Testing through: https://www.mail-tester.com

main cons for:

Delivered to internal network by a host with no rDNS
This may indicate you do not have a rDNS configured for your hostname or the rDNS does not match your sending IP - I wonder if this is the same as below? the same problem?
and also for:

"publish a DNS record (type A) for the host XXXXX.tehnodom.com or use a different host in the mail software." - How is that? what do I need to do on our VD server?

Answer 1

publish a DNS record (type A) for host XXXXX.tehnodom.com

on your DNS hosting, add an A record from the IP of the site from which the letters are sent.
(A) XXXXX.tehnodom.com - 11.22.33.44

Answer 2

G Suite has a limit of 500 emails per day, and we have big mailing lists!

Buy the commercial version and send more. All you need - $5 per month