What is the method used to share records owned by high-volume portal users?

The method to share records owned by high-volume portal users is through sharing groups. Sharing groups are specifically designed to provide a way to share records when there are multiple users who need access to the same records, particularly in a scenario involving high-volume portal users, such as customers or community members.

High-volume portal users often do not have the same sharing capabilities as regular Salesforce users due to their limited licenses, which restrict the use of certain sharing mechanisms. Sharing groups allow administrators to define a set of users who can access specific records, thereby ensuring that critical information is available to those who require it without needing to set up individual sharing rules for each record owner or user.

In contrast, record sharing rules are more suited for standard user profiles and may not align with the needs of high-volume portal users. Approval processes are designed for managing record validation and approval, rather than record sharing, and user permissions dictate access rights but do not inherently provide a mechanism for sharing records among a group of users. Therefore, relying on sharing groups is the most effective method for supporting high-volume portal users in accessing necessary records.