How did one email account expose Bank of Baroda's 1,000-GB of customer data?

Bank of Baroda said an employee's email account was compromised after a hacker claimed to leak 1,000 GB of data. A single corporate email account can act as a master key, unlocking internal networks, cloud backups and archived files via Single Sign-On. The account, possibly belonging to an auditor or IT administrator, may have allowed attackers access to internal repositories.