Date Modified changes on Selection on .eml file in AWS

We are having a problem with AWS Windows Server-2008 R2. When on Selection of a .eml file the Date Modified Changes. It also changes using Directory.GetFiles("directory_path") in C# code. This happens with this extension only. In local machine also we faced same issue and solved as per solution given here!.
We could not apply this solution on AWS server because of:

• The registry for .eml doesn't exists in said solution
• The 'Indexing Option' is not enabled in control panel.

Please suggest any solution. More details: We access the folder/files using GetDirectory and GetFiles (C#) to copy from one place to another based on last modified from stream of files in folder. Everytime after copying also, we get same files with latest timestamp.