This question is about an internally hosted SharePoint 2016 server. Information about how to do this with the SharePoint Cloud/SAAS is abundant and clear.
I would like to set up an internally hosted SharePoint 2016 server and allow users external to my domain (i.e. clients) to access sites on that server. I understand how to do the networking stuff. My question is about how to set up accounts with SharePoint that are for users that are not members of the domain SharePoint leverages.
The number of external users I allow access will be small per client, only one or two. Setting up a trust relationship or whatever between our organizations won't work.
Boiled down to as simple as I can get it, I want to tell SharePoint to grant access on "Site 1" to "the_product_owner@my_client.com". Or whatever the path is, preferably without giving that user an account on my network / domain.
I've burned quite a bit of time with various permutations of search terms to figure this out, and all I've uncovered so far is that it's super simple with SharePoint on the cloud and potentially impossible with SharePoint self-hosted.
Am I attempting the impossible? If not, could you please point me to information that describes how to do it?