When inspecting a file on disk in CData Arc, you will see that files that you see in the Administration console show a filename:

But if you look directly in the Receive folder for the connector on disk, an .eml file appears:

The contents of this eml contain not only the file contents, but a bunch of additional headers as well:

What is the .eml format: Files that are processed through CData Arc are stored in a message format while on disk, as detailed in the Architecture section of our product documentation at https://cdn.cdata.com/help/AZK/mft/Architecture.html#basic-message-structure
This eml format contains not only the contents of the file being processed, but also additional metadata about the content-type of the message, what it’s original filename is, what other connectors have processed this file and any additional metadata about the message that is used by the application to determine when to process the message, when messages have failed retrying, and any other metadata that is used to provide additional context to the message so it can be routed to other connectors in your flows.
Ordinarily, once a message leaves your flow, either via a transport connector that sends the file to another destination, or a File connector that drops the file off on the disk, all of this message context is removed and the “raw” file is transferred by the terminal connector in your flow:

The use of File connectors to drop off files on disk at the end of a flow is a recommended best practice in Flow design:
https://cdn.cdata.com/help/AZK/mft/Designing-a-Flow.html#best-practices
However, if a connector in your flow that is not a terminal connector outputs a message:

You will find that if you interact directly with the Receive folder on disk for that file, you will see messages written in that .eml format.
How do I prevent these files from appearing as .eml files on disk?
The recommended best practice in CData Arc is to incorporate the writing of a file to disk as part of your message flow as mentioned above. To do this, simply place a File connector at the end of your flow where the Path is set to the file on disk where the file is to be written:

Files sent through the File connector are written to the disk without the message context:


Alternatively, there is an option in the Advanced->Other Settings section of any given connector. If the configuration setting OutputFormat=raw is present in this configuration setting:

Files that are output to the Receive folder of this connector are written to disk in their raw format. In earlier releases of CData Arc (AS2 Connector V2 and V3 and RSSBus Connect) it was more common to interact directly with the folders on the file system, and connectors that are created in an earlier release will retain this setting:

I see that now but I have several eml files now that I want to restore to their raw format. How can I do that?
If you have several .eml files on disk that you want to remove the message envelope from and return them to their raw format, you can do the following:
1) Create a new File connector with the Send action:

and set the Path to a folder on disk that you want to output the raw files into:

You can use any path that you are able to write to so long as you are not using the Send folder of another connector in Arc (since Arc will be processing these files, it will return them to eml).
2) Pause the Send automation of this connector by unchecking the Send automation:

3) Move all emls that you want to convert on disk to the Send folder of the newly created File connector on disk. The full path to the Send folder will be based on the location of the Application Directory in CData Arc (https://cdn.cdata.com/help/AZK/mft/Windows-Edition.html#configuring-the-application-directory), the name of the connector and the workspace you are using.
For example, the default application directory for a new instance of CData Arc is C:\ProgramData\CData\Arc so for a connector named RestoreEML in the default workspace, that path would be:
C:\ProgramData\CData\Arc\data\RestoreEML\Send
NOTE: Newly created connectors do not automatically create folders on disk until they are needed, you should expect to see the full path except for the Send folder, and that can be created on disk manually.
4) Place the .eml’s you wish to convert into that path. When you are done, re-enable the Send automation to allow the application to process those files – they will be moved to the Path folder specified in the File connector with all message context removed.