How many people can receive notifications of my subscriptions?

The limit of users who can receive a notification depends on how your subscription is notified, but it is imposed by Google in both cases.

If you choose email notifications, the maximum number of users who can receive a notification (either in TO, CC or BCC ) is 100. However, if you are using Hangouts Chat notifications, the limit is the number of users who can be in the same room, which is 8,000.