For this server setup as the requirement of this setup, you have to take the VPS (virtual private servers), additional IPs (for IPs rotation) and domains.
VPS server will come as blank server and we will make those VPS servers as an SMTP server (after all the configuration) in order to send emails.
And after the configuration, these servers will be used for sending emails.
In technical term, we called them SMTP server which stands for Simple Mailing transfer Protocol Servers.
These SMTP servers will be connected with your mailing application for sending emails.
The number of servers will be depended on your server setup and how many emails you want to send.
If there are multiple servers then the system will automatically use them in rotation.