We have an open sources solution for Distribution Lists called Sympa, we are looking to migrate to Groups 365 or plained DL in exchange, but some features seems to be missing.
Is it possible for a Group365 to block members from unsubscribing ? the only way I found is to use the switch HiddenFromExchangeClientsEnabled : True but in doing so we loose the ability for owners to manage the membership :(
You cannot prevent them, they will still have an Unsubscribe link in any messages they receive, addressed to the Group. You can however use a script/flow/whatever to periodically re-add them as subscribers.