I have installed ISPConfig using the perfect server how-to for Ubuntu 20.04 LTS I have installed a domain and setup let's encrypt for it (I'm unsure if the certificate also covers the mail.mydomain.com subdomain) I have created a mailbox. I have also installed a phpBB3 forum, which I want to use SMTP to send emails problems: - I cannot login to the mailbox using POP3 over SSL on port 995 (message was that the server doesn't support the encryption type) - I could not send emails over SSL/TLS from my email client - test mails from phpBB3 could not be sent I have been using ISPConfig in the past, so I checked my postfix config files, but didn't see anything wrong. I have seen this how-to: https://www.howtoforge.com/tutorial/securing-ispconfig-3-with-a-free-lets-encrypt-ssl-certificate/ but I am unsure how to proceed. hostname -f on my system yields myserver.hostingprovider.com (I have no control over hostingprovider.com ) question : should I follow the steps described there regardless or should I change the hostname into myserver.mydomain.com ? what is the best way to solve my 3 problems ?