Get MIME mail content in Outlook Addin via Graph

Question

I am trying to create an outlook addin, that reads the selected mail in .MSG or .EML format. I found a Stackoverflow Question with a link to this documentation how to read a mail from Graph: https://learn.microsoft.com/en-us/graph/outlook-get-mime-message. I tried to use https://graph.microsoft.com/v1.0/me/messages/{id}/$value with the Graph tester. I entered all ids i could find in the Office.context.mailbox.item but none of them gave me a valid result. So where do I have to take the id from, the Graph Tester needs?

Answer 1

I found that: Office.context.mailbox.item.itemId.replace('/', '-').replace('+', '_'); gets the same id, the graph gives when asking for all messages via https://graph.microsoft.com/v1.0/me/messages. I just do not know why I have to replace chars in the id.