Abusing Exchange Mailbox Permissions with MailSniper

This report describes how Outlook/Exchange mailbox folder permissions (notably the "Default" entry) can be mistakenly set to allow organization-wide access, and shows how the MailSniper tool can enumerate and read such mailboxes across on-prem Exchange and Office365 using Invoke-OpenInboxFinder and a modified Invoke-SelfSearch; it includes examples, usage instructions, and remediation recommendations such as auditing mailbox permissions and applying GPO restrictions.