Why would you want to do this? Well, here is what Google says:
Forward an Email as an Attachments in Gmail
Attaching other emails to a message is a straightforward process. There are two ways to do it. First, you can select a message or messages from your inbox and click the Options menu (three dots) and choose Forward as an attachment.
Another way you can send them is by starting a new message, selecting the messages from your inbox, and then dragging them into the message box.
When you sent an email as an attachment it becomes a .eml file. And there is no limit on the number of emails you can attach. As the end-user, when you click on the .eml attachment the message will open in a new window. This new feature can help put an end to constantly forwarding messages and long and endless email chains. And organize both your inbox and make communication with others on your team easier. Note that this option is currently for G Suite users. Google also notes that this new feature is a gradual rollout. And there is no action required as an administrator. If you don’t see the option to “Forward as attachment” just hang tight as the feature will be coming soon. Time
