How to get MS365 Group email/message headers in Graph API or otherwise

Question

My main goal is to get the alias of an MS365 Group that an email was sent to, since in the toRecipients address, it resolves to the primary SMTP address. I have determined that the possible route I have to go to get this is through the email headers. This information appears in outlook when I click on "view message details" button in the email actions toolbar.

I've looked at the following questions:
Microsoft Graph : How get alias email from message
Find the email aliases a message was actually sent to
Microsoft Graph: How to get the alias from an email message?
Can you get PR_TRANSPORT_MESSAGE_HEADERS 0x007D from the .Net Microsoft Graph API?

However, when I try something like
https://graph.microsoft.com/v1.0/groups/{group-id}/threads/{thread-id}?$select=internetMessageHeaders&$expand=singleValueExtendedProperties($filter=id eq 'String 0x007D')
or
https://graph.microsoft.com/v1.0/groups/{group-id}/threads/{thread-id}?$expand=singleValueExtendedProperties($filter=id eq 'String 0x007D')

I get this error
Parsing OData Select and Expand failed: Could not find a property named 'singleValueExtendedProperties' on type 'microsoft.graph.conversationThread'

Answer 1

ConversationThread is an object that represents that whole thread of a conversation which main contain one or many messages (or they are refereed to as posts). So you need to first get all the associated posts /groups/{groupId}/conversations/{conversationId}/threads/{threadId}/posts. Then using the Id of a particular post that you are interested eg

GET /groups/{id}/threads/{id}/posts/{id}?$expand=singleValueExtendedProperties($filter=id eq '{id_value}')
GET /groups/{id}/conversations/{id}/threads/{id}/posts/{id}?$expand=singleValueExtendedProperties($filter=id eq '{id_value}')

ref https://learn.microsoft.com/en-us/graph/api/singlevaluelegacyextendedproperty-get?view=graph-rest-1.0&tabs=http and https://learn.microsoft.com/en-us/graph/api/resources/post?view=graph-rest-1.0