I'm trying to send a email which contains another email in its attachments with a EWS request but I'm struggling with it... I have the information about the the email's id which must be attached as its id.

First, I tried to create the email with the attachment in it :

The subject
The body






mailTo

But it doesn't work and I have the error : "Set action is invalid for property - ErrorInvalidPropertySet" for the FieldUri : item:Attachments"

After that, I tried to create an attachment to attach to the mail that I have created with "SaveOnly" (so I got the Id and the ChangedKey of it) :

  
    
      
      
        
          
false
        
      
    
  

And it failed too with the error : "An item must be specifed when creating an item attachment - ErrorMissingItemForCreateItemAttachment"

I'm not sure where I had to specifed the email's id I try to attach and it is may be here that my problem is (Id, or RootItemId).