I've reviewed the CSF.conf file and noticed all the ports are listed in TCP and TCP6 in/out. I noticed this section: SMTP_PORTS = "25". I've tried 465, 587 and still getting the message in XenForo "couldn't open socket".. I've restarted CSF as well. Any hints? Open Port Check Tool - Test Port Forwarding on Your Router tells me the port is closed as well.
Maybe this command helps? Shows the port is listening however still XenForo gives me the socket error. A few port checker websites tell me it's still closed.
Check official CSF firewall page for Centmin Mod at CSF Firewall - CentminMod.com LEMP Nginx web stack for CentOS You only need outbound TCP/TCP6 ports open for using 3rd party SMTP transactional email providers to send from Xenforo. That is why that web site port checker says closed as the inbound ports are whitelisted on Centmin Mod servers via /etc/csf/csf.conf config but Centmin Mod doesn't setup inbound postfix so of course that web site can't connect to your server. But you should be able to send via Xenforo SMTP specified host if you have the correct SSL or TLS and port SMTP setting provided by your SMTP provider.
Ended up having to use Port 587, TLS option, and re create all new Creds in AWS. So far so good right now.