i have recently installed CyberPanel on my home lab to create a mailsrv. i have setup the DNS on cloudflare and check the port on the srv / firewall with nmap, i have also check the journalctl but could not find a way to fix it.
First of all remove cloudflare proxy and then check again
I have done that but nothing changed
If you use residential internet connection, they might restrict some ports what used for mails.