Summary
There is no way to define a server- or domain-wide default disk quota that is automatically applied when a new user account is created. Today, maxDiskQuota must be set explicitly on each Account, which is error-prone in declarative deployments and incompatible with a smooth OIDC onboarding flow.
Problem
We operate Stalwart external authentication (OIDC / Keycloak). We want every mailbox to have a default storage limit (e.g. 1 GiB per user) without manually setting quotas on each account.