Servers handle command and application execution differently, depending on the operating system. From a security perspective, executable files should be tightly controlled. Only the server administrator should be allowed to install and run executables, and the server should not respond to file execution from within unauthorized directories.
On a Windows server, file executables typically have .exe, .com, or .bat extensions. Without question, any emails or other transfers that contain such attachments should be blocked. Many attackers have adapted to mail scanners that block those extensions and will often send files with alternative extensions like .zip, but the files are still actually executables. You can decide what types of files to restrict and how to scan and monitor incoming files.
On a Linux server, any file can potentially be executable when it is assigned the correct permissions. In fact, standard executables have no file extensions at all. This means you have to be extra cautious about unauthorized scripts. You can deny executable privileges to any directories/partitions except the ones owned by root. This should greatly reduce the chances of security exploits. Usually, a Linux mail server will still receive Windows virus executables intended for home Windows computers. You should, therefore, configure a mail scanner to detect them and quarantine them.
Photo Source: Flickr