Several questions concerning CI4 controller

Anything concerning the issue with the Certificates for the email server?

The SSL certificates must be installed in Postfix which requires some edits to the Postfix configuration file. After that, the CodeIgniter config setting SMTPCrypto is the most important for your needs, e.g.

PHP Code:

public $SMTPCrypto = 'tls'; 


And of course, you need to set all the other SMPT* config items as appropriate for your Postfix setup.