Two IPs, DNS records and Spam emails

[Deivis]

I have a VPS with Plesk 12.0.18 Update #80 under Debian 7.9 and i'm new on this. I've been experienced troubles with my out-going messages (fall in SPAM FOLDER or even do not arrive to destination). I think that is a problem with my DNS records or something. I attach a picture of my DNS records. There is something that result confuse to me, is that I have two IPs, one that is 172.31.1.100 which is private and the other that is public, I don't know what IP use in the DNS, i guess that is the public and now is configured using this IP, but i don't know if is correctly configured. All services work fine except the email server, always when I send a email, it goes to the spam folder o not arrive to the destination. I need some help to fix that problem.