docs/data/reusables/billing/email-notifications.md

Email notifications are sent to account owners and billing managers when spending reaches 50%, 75%, 90% and 100% of your account's included usage and when spending reaches 50%, 75%, 90%, and 100% of your account's spending limit.

You can disable these notifications at any time by navigating to the "Email alerts" section at the bottom of the "Spending limit" page.