Great question! We achieve this by using a top-level grouping mechanism for all mail sent through Helo (called "Channels"). Every message sent must be associated with a Channel, and this is typically how you would organise your tenants (one per Channel).
This allows us to track deliverability signals separately for each tenant, regardless of the sending domain they happen to be using. When we see signs of suspicious behaviour or poor sending practices (ie. bounces, spam complaints), we can pause sending for individual tenants before they cause problems for the entire set of senders using that domain (and the platform as a whole).