Accessing headers of body part in multipart mail in Outlook using C#

Question

I am trying to extract the headers of the body part of a multipart mail message in Outlook. The raw message (which I have not been able to get from my code) looks something like this:

Return-Path: ...
Received: ...
From: ...
Content-Type: multipart/signed; boundary="Apple-Mail=_06FDFEBB-366E-4B1E-AA7F-F5DDEC13FD03"; protocol="application/pgp-signature"; micalg=pgp-sha512
Subject: ...
Message-Id: ...
Date: ...
To: ...
Mime-Version: ...
X-Mailer: ...


--Apple-Mail=_06FDFEBB-366E-4B1E-AA7F-F5DDEC13FD03
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
    charset=us-ascii

...

--Apple-Mail=_06FDFEBB-366E-4B1E-AA7F-F5DDEC13FD03
Content-Transfer-Encoding: 7bit
Content-Disposition: attachment;
    filename=signature.asc
Content-Type: application/pgp-signature;
    name=signature.asc
Content-Description: Message signed with OpenPGP using GPGMail

...

--Apple-Mail=_06FDFEBB-366E-4B1E-AA7F-F5DDEC13FD03--

I have replaced some of the none relevant parts by dots. The headers I am trying to get are the ones under the first boundary. So this is the part I am looking for:

Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
    charset=us-ascii

However, if I could get the entire part between the boundaries, that would also be fine as I could parse it myself.

So far, I have only been able to get the headers at the top of the message (so from Return-Path until X-Mailer ). I was able to do that using a `PropertyAccessor in the following way:

mailItem.PropertyAccessor.GetProperty("http://schemas.microsoft.com/mapi/proptag/0x007D001E")

In this case mailItem is my Microsoft.Office.Interop.Outlook.MailItem instance.

So, what my question comes down to: How can I get the headers under the first boundary, or any bigger part of the message that contains them?

Answer 1

PR_TRANSPORT_MESSAGE_HEADERS property is the only thing you can get. Outlook does not store the full MIME source of the original message.

You can see what is available in OutlookSpy - click IMessage button.

Answer 2

For signed messages, Outlook preserves the signed message body (with full MIME data) in an attachment called smime.p7m (it's always called smime, even if it's actually PGP/MIME). Unfortunately, Outlook hides this from you, transparently unpacking the signed message and displaying it instead. There's no way, using the Outlook Object Model, to get the actual message body.

However, if you're willing to call MAPI directly (easiest from native code, but can be done from .NET if you're not afraid of some nasty COM interop), you can get the multipart/signed body - both the signature and the complete signed part - as follows:

Starting from the Outlook MailItem , get the MAPIOBJECT property. This is actually a MAPI IMessage . Cast it to an IMAPISecureMessage (.NET will handle this as a QueryInterface behind the scenes). Call GetBaseMessage() on this IMAPISecureMessage (the only documented function), which returns another IMessage . This is the "real" message, the one with the smime.p7m attachment. Unfortunately, there's no way to put this back into OOM, so you have to continue using MAPI. By calling the functions on IMessage , you can get the attachment, then get its data. You'll need to parse the MIME parts, at least enough to get the signed part without its headers, outer boundaries, or of course the signature part. Verify that signed part ( without decoding its internal parts, if any, or decoding quoted-printable or anything like that) against the signature blob.