I have server disks from a Linux system. Linux has crashed. I would like to know how to check where the mails are stored in the system (probably postfix). I can only view files in Windows - the Linux system is not functioning.
You will need something that can read the file system of the Linux server. That is actually hard on Windows, because there are not great drivers available. You might do better with a "LiveCD" style bootable Linux system.
To read the disk you need something that can understand the file system. Since you don't specify a distribution, the most likely format is ext3, or perhaps ext4, for which a Windows ext2 IFS driver or a user-space tool that reads the file system are the best bet.
Once you have access to the disk, Postfix stores email in
/var/spool/postfix, in a binary format that you really want the postcat(1) tool to extract in human readable format. The basic data is plain enough text, though.
The configuration of Postfix, which can - but rarely does - override the configuration is in
/etc/postfix on a typical system.