is there a definitive guide on the topic as it relates to virtualmin?
The auto-configuration files are provided in Virtualmin > System settings > Server templates > Mail client auto-configuration. You may need to fine tune the settings.
You will also need some DNS records and I am using GitHub - Incruises/autodiscover.xml: Provides Autodiscover capabilities for IMAP/SMTP services on Microsoft Outlook/Apple Mail and Autoconfig capabilities for Thunderbird as a guide. It covers the different auto-configuration requirements of Microsoft, Apple, iOS and Thunderbird.