Gartner Research: One minute downtime can cost around $5600 on average, depending on the size of the business. Exchange downtime can impact productivity and lead to data loss that can have severe implications on your business. Its important to maintain backups and implement best practices for Exchange servers that can help restore the Exchange server when a disaster strikes with minimal impact and downtime. To prevent malicious attacks, such as Hafnium, you must install the Exchange Server and Windows Server updates as they arrive.”]
Source: https://threatpost.com/how-to-reduce-exchange-server-downtime/168344/