从IMessage获取Outlook.MailItem

Question

I'm working on an Outlook add-in (VSTO, C#) that needs to be able to access the smime.p7m file from a signed or encrypted message. I know how to get the relevant IMessage , but I'm hoping to do this in C# without needing to implement too many COM wrappers. Here's what I've got so far:

I wrote a C# wrapper for IMAPISecureMessage . It's not long or complex. I can take an Outlook.MailItem and get its MAPIOBJECT property, which appears to just be the underlying IMessage . I can then cast that IMessage to my IMAPISecureMessage wrapper and call GetBaseMessage() on it. This all appears to work.

The problem is, this returns an IMessage . I need to extract the attachment (smime.p7m) from this IMessage . I was hoping I could do that by wrapping a MailItem around the returned IMessage , but I can't find any way to do that. I can see how to create a MailItem ( Application.CreateItem or Items.Add ), but I can't set the MAPIOBJECT property of an existing MailItem , and I don't see a way to create a MailItem from an existing MAPI object (such as my IMessage from GetBaseMessage() ).

Is there a way to do create the desired MailItem ? If not, is there a way I can get the attachment (smime.p7m) out of the IMessage without either implementing a whole bunch of COM interfaces or using a proprietary third-party library (such as Redemption)?

Answer 1

You could of course create IMessage , IMAPITable , IAttach interface definitions and call IMessage::GetAttachmentTable , then IMAPITable::SetColumns / QueryRows (or HrQueryAllRows ) to retrieve PR_ATTACH_NUM , then call IMessage::OpenAttach to open the attachment, then IAttach.OpenProperty(PR_ATTACH_DATA_BIN, IID_IStream, ...) to open the binary data as IStream .

You can also try to change the message class of the message to IPM.Note , save it, completely release (and pray Outlook does not keep a reference), then open it as a regular MailItem using Namespace.GetItemFromID .

Or, as you mentioned, you can use Redemption and its RDOEncryptedMessage object.