Accessing Message Attachments

#include <afxwin.h>
#include <edk.h>

int main()
{
    /*
     * Algorithm:
     *  1. Open the message.
     *  2. Open its attachment.
     *  3. Create a file and store PR_ATTACH_DATA_BIN in it.
     */

    // Change if necessary
    char * pszFolder = "@PR_IPM_SUBTREE_ENTRYID\\Drafts";
    char * pszMsgSubject = "Message with Attachment";
 
    HRESULT hr;
    LPMAPISESSION pSession = NULL;

    // Initialize MAPI
    hr = MAPIInitialize(NULL);
    if (FAILED(hr)) throw -1;

    // Obtain MAPI session
    hr = MAPILogonEx(0,    // Handle to parent window
      "MS Exchange Settings", // Profile name
      NULL,   // Password
      MAPI_NEW_SESSION |
      MAPI_EXTENDED |
      MAPI_LOGON_UI, // Logon flags
      &pSession);  // Resulting MAPI session
    if (FAILED(hr)) throw -1;

    // Find default message store
    ULONG cbDefStoreEid = 0;
    LPENTRYID pDefStoreEid = NULL;
    hr = HrMAPIFindDefaultMsgStore(pSession, &cbDefStoreEid, &pDefStoreEid);
    if (FAILED(hr)) throw -1;

    // Open default message store
    LPMDB pDefMsgStore = NULL;
    hr = pSession->OpenMsgStore(0, cbDefStoreEid, pDefStoreEid, NULL,
        MDB_WRITE | MAPI_DEFERRED_ERRORS, &pDefMsgStore);
    if (FAILED(hr)) throw -1;

    // Open the desired folder
    LPMAPIFOLDER pFolder = NULL;
    hr = HrMAPIOpenFolderEx(pDefMsgStore,
       '\\',
       pszFolder,
       &pFolder);
    if (FAILED(hr)) throw -1;

    // Get contents table.
    LPMAPITABLE pContentsTable = NULL;
    hr = pFolder->GetContentsTable(0, &pContentsTable);
    if (FAILED(hr)) throw -1;

    // Get row count
    ULONG ulRows = 0;
    hr = pContentsTable->GetRowCount(0, &ulRows);
    if (FAILED(hr)) throw -1;
    assert(ulRows > 0);

    // Get all rows
    SRowSet * pRowSet = NULL;
    hr = pContentsTable->QueryRows(ulRows, 0, &pRowSet);
    assert(ulRows == pRowSet->cRows);

    // Scan all rows until we have our source message
    SRow row;
    LPUNKNOWN pMsg = NULL;
    ULONG ulObjType = 0;
 
    for (ULONG ul = 0; ul < ulRows; ul++)
    {
        row = pRowSet->aRow[ul];

        for (ULONG ulIndex = 0; ulIndex < row.cValues; ulIndex++)
        {
            if (PR_SUBJECT == row.lpProps[ulIndex].ulPropTag)
            {
                char * pszCurSubject = row.lpProps[ulIndex].Value.lpszA;
                int iRes = memcmp(pszMsgSubject, pszCurSubject, strlen(pszMsgSubject));
                if (0 == iRes)
                {
                    // We have found our message!
 
                    // Get PR_ENTRYID
                    SBinary bin;
                    ZeroMemory(&bin, sizeof(bin));
                    for (ULONG ulNewIndex = 0; ulNewIndex < row.cValues; ulNewIndex++)
                    {
                        if (PR_ENTRYID == row.lpProps[ulNewIndex].ulPropTag)
                        {
                            bin = row.lpProps[ulNewIndex].Value.bin;
                            break;
                        }
                    }
                    assert(bin.cb);
 
                    // Open the message
                    hr = pDefMsgStore->OpenEntry(bin.cb,
                        (LPENTRYID) bin.lpb,
                        NULL,
                        MAPI_BEST_ACCESS,
                        &ulObjType,
                        &pMsg);
                    if (FAILED(hr)) throw -1;
                }
            }
        }
    }
    // At this point we have the message open...

    // Open its attachment
    LPMAPITABLE pAttachTbl = NULL;
    hr = ((LPMESSAGE) pMsg)->GetAttachmentTable(0, &pAttachTbl);
    if (FAILED(hr)) throw -1;

    // Get row count
    hr = pAttachTbl->GetRowCount(0, &ulRows);
    if (FAILED(hr)) throw -1;
    assert(1 == ulRows);

    // Get all rows
    if (pRowSet)
        MAPIFreeBuffer(pRowSet);
    pRowSet = NULL;
    hr = pAttachTbl->QueryRows(ulRows, 0, &pRowSet);
    assert(ulRows == pRowSet->cRows);

    // Get PR_ATTACH_NUM
    row = pRowSet->aRow[0];
    LPATTACH pAttach = NULL;
    ULONG ulAttachNum = 0;
    for (ULONG ulIndex = 0; ulIndex < row.cValues; ulIndex++)
    {
        if (PR_ATTACH_NUM == row.lpProps[ulIndex].ulPropTag)
        {
            // Open the attachment.
            ulAttachNum = row.lpProps[ulIndex].Value.l;
            hr = ((LPMESSAGE) pMsg)->OpenAttach(ulAttachNum,
                 NULL,
                 MAPI_BEST_ACCESS,
                 &pAttach);
            if (FAILED(hr)) throw -1;
            break;
        }
    }
    // At this point we should have the attachment open

    // Get PR_ATTACH_DATA_BIN property
    SPropTagArray tagArray;
    tagArray.cValues = 1;
    tagArray.aulPropTag[0] = PR_ATTACH_DATA_BIN;

    ULONG ulValues = 0;
    LPSPropValue pAttachDataBin = NULL;
    hr = pAttach->GetProps(&tagArray,
       0,
       &ulValues,
       &pAttachDataBin);
    if (FAILED(hr)) throw -1;
    assert(pAttachDataBin);

    // Create a file to write data to
    HANDLE hFile = CreateFile("C:\\AttachData.txt",
        GENERIC_WRITE,
        0,
        NULL,
        OPEN_ALWAYS,
        FILE_ATTRIBUTE_NORMAL,
        NULL);
    assert(hFile != INVALID_HANDLE_VALUE);

    // Save data
    DWORD dwBytesWritten = 0;
    BOOL b = WriteFile(hFile, // Handle to the file
      pAttachDataBin->Value.bin.lpb, // Pointer to data to write to file
      pAttachDataBin->Value.bin.cb, // Number of bytes to write
      &dwBytesWritten,    // Number of bytes written
      NULL);       // Pointer to OVERLAPPED structure
    assert(b && (dwBytesWritten == pAttachDataBin->Value.bin.cb));
 
    // Cleanup
    if (hFile)
        CloseHandle(hFile);
    if (pAttachDataBin)
        MAPIFreeBuffer(pAttachDataBin);
    if (pAttach)
        pAttach->Release();
    if (pAttachTbl)
        pAttachTbl->Release();
    if (pMsg)
        pMsg->Release();
    if (pRowSet)
        MAPIFreeBuffer(pRowSet);
    if (pContentsTable)
        pContentsTable->Release();
    if (pFolder)
        pFolder->Release();
    if (pDefMsgStore)
        pDefMsgStore->Release();
    if (pDefStoreEid)
        MAPIFreeBuffer(pDefStoreEid);
    if (pSession)
        pSession->Release();
    ::MAPIUninitialize();
    return 0;
}

The algorithm is straightforward. I assume that the message resides in the Drafts folder, has "Message with Attachment" subject, and in fact contains 1 attachment.