I'm gonna go with Chatgpt on this one:
The model that the company should choose to move its on-premises corporate email systems to a multitenant product hosted in the cloud where no maintenance of the underlying server OS or platform is required is the Public cloud model. The public cloud is a type of cloud computing where cloud-based services and resources are provided over the internet to anyone who wants to use or purchase them. In this model, the resources are owned, managed, and maintained by a third-party cloud provider, who is responsible for the infrastructure, underlying server OS, and platform maintenance, leaving the customer free to focus on their application or service. This option provides the greatest degree of scalability, flexibility, and cost-effectiveness while reducing management overhead.