Mail Message header request returns incomplete data?

Am using the following call to attempt to pull the full header off an email message stored in an Exchange Online user's mailbox:

https://graph.microsoft.com/v1.0/users/<user UPN>/mailFolders/<mail folder ID>/messages/<mail message ID>=?$select=Subject,InternetMessageHeaders

I receive back most of the header information.  Strangely, what is missing is the one piece of information that I am looking for which is the "To".  The reason I am trying to pull it this way is that once the message lands in its destination EOL is resolving the To field to items from Address Book.  I don't want this but rather the original contents of the message's To field.