==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release): 1.0
- Deployed with iRedMail: Downloadable
- Linux/BSD distribution name and version: Ubuntu 18.4
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): mysql
- Web server (Apache or Nginx):nginx
- Manage mail accounts with iRedAdmin-Pro? No
====

I have iredmail deployed at my home, it works great,  but my problem lies on my dedicated server I'm renting.

At home: Incoming mail works &shows all connection logs, failures, etc

On the Dedicated Server: Mail from outlook.com comes in fine, the logs are there I can connect to the smtp port.

BUT mail from gmx.com doesnt come in at all, no connection logs, and cannot connect to the smtp port. This problem is happening with multiple domains, but not all of them.

Also: I havent successfully sent mail to gmx.com from the dedicated machine and also my ip IS NOT located on any blacklists, my MX records are all good, I have ssl and all ports working.

Why is mail.log not showing all connection attempts or blocks? IT LOOKS like an ip ban but that isnt possible, I have even changed domain name & host ip in the process to trouble shoot this.

Once again, my home mail server receives just fine, yet the other server isnt showing all of the incoming connections & requests for mail and is not receiving from all domains.

What makes a domain not want to send mail to you if you have never sent mail to it? I know the basic answers but would like your expert option.

Thank you for your time and input Zhang!