How can user accounts be synchronized across different systems?

User accounts can be effectively synchronized across different systems through directory synchronization tools. These tools automate the process of ensuring that user information, such as usernames, passwords, and permissions, is consistently updated and maintained across various platforms and applications. This not only saves time and reduces errors associated with manual updates but also enhances security by ensuring that policy changes or updates are uniformly applied.

In contrast, manually updating each account could lead to inconsistencies and is impractical for organizations with large numbers of users. Email notifications serve to inform individuals about changes but do not synchronize data. Banning users from multiple systems doesn't contribute to synchronization and would instead limit access and functionality across important applications used by the users. Thus, directory synchronization tools are the most efficient and reliable method for maintaining user account consistency across systems.