Get ContentId (or any FileAttachment properties) without ContentBytes with Outlook REST API

Question

In my application that uses the Outlook REST API, in order to support inlined images in html emails, I need to retrieve the ContentId of the File Attachments of a given email.

Note: in an html email inlined images are html tags of the form <input scr="cid:mycontentid">

I manage to get this information at url https://outlook.office.com/api/v2.0/me/messages/{message_id}/attachments

The problem is the returned json also contains the ContentBytes which can be arbitrary big for large attachments.

I tried several syntaxes to retrieve only the fields that I need such as:

https://outlook.office.com/api/v2.0/me/messages/{message_id}/attachments?$select=Id,ContentId or '$select=Id&$expand=ContentId'

none of them worked, resulting in a bad request

{"error":{"code":"RequestBroker-ParseUri","message":"Could not find a property named 'ContentId' on type 'Microsoft.OutlookServices.Attachment'."}}

The expected types at url '/attachments' are Microsoft.OutlookServices.Attachment which is a base type for File Attachments and Item Attachment.

I would like to retrieve the specific member for File Attachments (ContentId) or to discard the heavy ContentBytes contained in the result.

Answer 1

The endpoint of me/messages/{message_id}/attachments return the collection of attachment.

The ContentId is the property of FileAttachment. You can use the code below to get the contentId of fileAttachment:

GET: https://outlook.office.com/api/v2.0/me/messages/{messageId}/attachments?$select=Microsoft.OutlookServices.FileAttachment/ContentId

EDIT: Remark: if you want to retrieve other field, say Name note that $select=Microsoft.OutlookServices.FileAttachment/ContentId,Name will work while that $select=Name,Microsoft.OutlookServices.FileAttachment/ContentId will throw the error mentioned in the original question