The preinstalled mail server by IONOS is usually enough for beginners and private users to get started immediately. Anyone needing more options can install open source software like PostFix to set up their own mail server. They will need a Linux operating system and root permissions for the server. But that’s no problem, as the IONOS VPS runs on both Windows and Linux operating systems and allows the necessary root access.
Microsoft offers software licenses through a program called the Service Provider License Agreement. The SPLA model provides use of Microsoft products through a monthly user or processor based fee. SPLA software includes the Windows Operating System, Microsoft SQL Server, Microsoft Exchange Server, Microsoft SharePoint and shoutcast hosting, and many other server based products.
The answer to this question largely depends on two factors. Are you new to server technology and not very interested? In this case, Windows is the easiest option to get where you want to go. Do you already have experience with Linux or would you like to familiarize yourself with this operating system? If so, Linux gives you more freedoms to configure your server, and you will be using an operating system that is less vulnerable to attacks from the Internet. Linux is also open source and therefore free.