Hi Till & Team I am trying to open a port on one of my servers in my MultiServer setup, I have added the port to the firewall rules in the Server setup in ISPConfig / System / Firewall, but a port scan on MXToolbox reveals that the port remains closed. Can anyone please advise how i can get this port opened (443 on a mail server - i'm following the guide here https://www.howtoforge.com/community/threads/letsencrypt-on-mail-server.73695/#post-349372 to add Lets Encrypt to my mail servers)
Check that you're not blocking it on the router. If you're using only 1 public IP with the multiserver setup, you're probablly routing port 443 to the webserver for https websites.
