How to Forward a Message as an Attachment With Windows Mail
To forward an email attached to a new message in Windows Mail:
Highlight the message you want to forward in the mailbox or open it in a separate window. Select Settings (the three-dot menu), then choose Save As. Save the message in EML format. Compose a new message by clicking or tapping New mail, then advance the toolbar to the Insert menu in the message pane. Select Files, then choose the EML document you saved. Select Open to insert the message as an attachment inside the new email. Compose and send your email as usual.
This process is not technically the same as the Forward As Attachment command, but the result is the same.
