Looks like a network/firewall issue.
MX Toolbox cannot connect, same message as in @ETNyx ’s post.
I also tried via nmap, and it says port 465 is filtered…
Host is up (0.14s latency).
PORT STATE SERVICE
465/tcp filtered smtps
So it looks like port 465 incoming is being filtered by a packet filter/firewall, either directly on the OS where Mailcow is installed, with something like UFW, Firewalld, or (rather unlikely if you have not proactively changed anything) directly in nftables or iptables. Or if you are hosting on a VPS, the VPS provider may have a firewall in front of their VPSs where you have to open port 465. Or, and that would be the worst case, the VPS provider generally blocks email ports, in which case you would need to contact them.