There are several reasons why it is necessary to have a third-party backup of Microsoft 365. Some of these reasons include:

Data loss prevention: Microsoft 365 includes tools and features for data backup and recovery, but it is still possible for data to be lost due to user error, hardware failure, or other unforeseen events. A third-party backup solution can help ensure that data is protected in the event of a data loss event.

Compliance with regulations: Depending on the nature of the business, it may be necessary to comply with regulations that require the use of a third-party backup solution. For example, the Payment Card Industry Data Security Standard (PCI DSS) requires businesses to maintain a secure copy of their data in the event of a disaster or data loss.

Business continuity: A third-party backup solution can help ensure that a business can continue to operate in the event of a disaster or data loss event. By having a backup of their data, businesses can minimize downtime and maintain productivity.

Increased security: A third-party backup solution can provide an additional layer of security for Microsoft 365 data. By having a separate, secure copy of the data, businesses can protect themselves against potential data breaches or other security threats.

Overall, it is necessary to have a third-party backup of Microsoft 365 due to data loss prevention, compliance with regulations, business continuity, and increased security. By implementing a third-party backup solution, small businesses can better protect their data and ensure that they can continue to operate in the event of a disaster or data loss event.