如果附件本身是邮件，如何在 Outlook 中以编程方式访问附件数据

Question

I am programmatically trying to get the attachment data in C# in following way :--

Microsoft.Office.Interop.Outlook.Attachment attachment = objMail.Attachments[attachmentIndex];

if (attachment.DisplayName.Equals("Test"))

{ 

   const string PR_ATTACH_DATA = "http://schemas.microsoft.com/mapi/proptag/0x37010102";

    byte[] attachmentData = attachment.PropertyAccessor.GetProperty(PR_ATTACH_DATA);

}

Now my code is working fine if attachment is text file or image file. But if attachment is itself a mail, it throws the exception that property is unknown or can not be found.

Please suggest in which cases / type of attachments, this property " http://schemas.microsoft.com/mapi/proptag/0x37010102 " will not work and in those cases, what would be alternative property / method to get the attachment data in byte array ?

Thanks

Answer 1

PR_ATTACH_DATA_BIN is only present for the regular by-value attachments ( PR_ATTACH_METHOD == ATTACH_BY_VALUE ). Embedded message or OLE attachments do not expose that property - they use PR_ATTACH_DATA_OBJ which must be opened using IAttach::OpenProperty(IID_IStorage, ...) - take a look at the existing messages using OutlookSpy (select the message, click IMessage button, go to GetAttachmentTable tab, double click on the attachment).

Also keep in mind that PropertyAccessor.GetProperty would only be able to retrieve that property for small attachments. For large attachments, PR_ATTACH_DATA_BIN must be opened as IStream using IAttach::OpenProperty(IID_IStorage, ...) - PropertyAccessor.GetProperty does not do that. You will need to use Extended MAPI (C++ or Delphi) or Redemption (which exposes RDOAttachment . AsArray / AsText / AsStream properties.

Answer 2

Microsoft Graph Rest API is an single end point and wrapper for most Microsoft Data including events, most office products including outlook. Best of all any language can make a request to the endpoint and retrieve the information. See the complete Docs HERE to get started.

See below code for a simple Get request for outlook attachments. Note there are other more complex implementations. Docs: https://docs.microsoft.com/en-us/graph/api/attachment-get?view=graph-rest-1.0&tabs=http Scroll through the link and you can find C#, Java, and JavaScript examples on how to implement this.

GET /me/messages/{id}/attachments/{id}
GET /users/{id | userPrincipalName}/messages/{id}/attachments/{id}

GET /me/messages/{id}/attachments/{id}/$value
GET /users/{id | userPrincipalName}/messages/{id}/attachments/{id}/$value