i don't know about CDO and M$ Exchange Server & Client application.
if problem is file locking that use AddAttachment, how about use temporary file name?
generate the temporary file name every time, it is a one of solution that i think.

alex 님이 쓰신 글 :
: The file("c:\\filename.txt" ) i used for attachment cannot delete until the application terminated..
:
: Is there anyway i can delete it?  Is it suppose to work this way???
: Thanks in advance..
:
:
:     CDO::IBodyPart* pIBodyPart = NULL;
:     if ( SUCCEEDED(  m_pIMessage->AddAttachment( L"c:\\filename.txt",L"",L"",&pIBodyPart )
:     {
:                 hr = pIBodyPart->put_ContentMediaType( _bstr_t( "text/plain" ) );
:                 std::string  strDisposition ="attachment;filename=" ;
:                 strDisposition += SZ_FILTERFILE ;
:                 {
:                     Field*  pField = NULL;
:                     Fields* pFields = NULL;
:                     hr = pIBodyPart->get_Fields( &pFields );
:                     // Disposition.
:                     hr = pFields->get_Item( _variant_t( "urn:schemas:mailheader:content-disposition" ), &pField );
:                     _bstr_t bstrDisposition( strDisposition.c_str() );
:                     hr = pField->put_Value( _variant_t( bstrDisposition ) );
:                     pField->Release();
:                     pField= NULL;
:                     hr = pFields->Update();
:                     pFields->Release();
:                   
:                 }
: }