Setting up SSL TLS for Sentora Mail - Centos 7

[Qtech]

Hello I have Centos 7 server with Sentora.

I am trying to setup SSL for mail services.
Is there a full guide for Centos 7

I did read this http://forums.sentora.org/showthread.php?tid=46
but then I got confused about the DNS

I have 5 domains that I host.

Main domain for Sentora is set up as name.domain_main.net

I have DNS like this.
MX 10 mail.domain.com
TXT for Google verification for each domain

on domain_main.net
SPF v=spf1 ip4:xxx.xxx.xxx.xxx -all
MX 10 mail.domain_main.net

# 1. Is my MX for each domain incorrect?
# 2. Is there full guide for SSL for Centos 7
# 3. Should I do a sell signed Certificate?
# 4. On my Server Admin > Sentora Config what should I change for Mail settings?

Thanks.