Add controls to enable/disable individual services and to customize autodiscover settings

[xander]

From a security standpoint, it would be really useful if we could disable services which we are not using.

For example, many people no longer use POP3. While we can block the relevant ports on the firewall, it would be nice if we could actually disable the listeners themselves so that Posteio is aware we are not using them.

A current knock-on effect of this is that the POP3 details are automatically added to the server’s autodiscover.xml regardless of whether we intend to use the service.

In addition, various other settings such as default ports and encryption schemes are automatically populated into the autodiscover.xml file. Currently these default to the implicit TLS ports, but some of us may wish (or need) to change these settings.

A possible “simple” solution for this would be a page listing each service, with an option to enable/disable it, and (where appropriate) a checkbox to allow us to select if the service should appear in the autodiscover.xml file.

Many thanks for the awesome software!