Groups IO
Groups IO came to the forefront around 2019 with the dismemberment of Yahoo Groups, however they have been around since 2014. Initially the platform offered free and robust features but by 2020, they introduced a pricing structure and severely limited the features of their basic group. 

Still, for many chapters, either a Basic (free) or a Premium account (per month) is budget worthy. A Premium account comes with Subgroup options. For larger chapters that means every one of NGs/SIGs and their Chapter Advisory Board (CAB) can have their own communication forum group at no additional cost. 

It is a somewhat complex platform to administer. On the plus side there are extensive online help manuals and at least twousergroupsdedicatedtoassisting group owners in a very timely manner. 

https://groups.io/g/GroupManagersForum

https://groups.io/g/Group_Help

Workpace Groups (WG) offered by Google operates the same as Google Groups with very little change since 2010. Attachments are stored on the server and accessible in searches. Subscriptions can be set to individual which makes delivery timely. Members can be directly added and do not need to be adomainuser. Any personal email address can be added. A footer is required giving members the ability to unsubscribe.

The WG posting address is of your own choosing and will end in your domain name. This means it iseasily recognized by your board and members as coming fromalegitimatesource. 
On the downside is that support comes through Community Forums and that means questions may not be answered in a timely or robust fashion.