By default, this playbook configures an mxisd Identity Server for you.
This server is private by default, potentially at the expense of user discoverability.
To ensure maximum discovery, you can make your identity server also forward lookups to the central matrix.org Identity server (at the cost of potentially leaking all your contacts information).
Enabling this is discouraged and you'd better learn more before proceeding.
Enabling matrix.org forwarding can happen with the following configuration:
matrix_mxisd_matrixorg_forwarding_enabled: true
What this playbook configures for your is some bare minimum Identity Server functionality, so that you won't need to rely on external 3rd party services.
Still, mxisd can do much more. You can refer to the mxisd website for more details.
You can override the matrix_mxisd_template_config
variable and use your own custom configuration template.
If email address validation emails sent by mxisd are not reaching you, you should look into Adjusting email-sending settings.