private void AttachSalesLiteratureItemsToEmail(ICrmService service, Guid SalesLiteratureID, Guid EmailID, ref CrmNumber attachNo)
{
    // condition
    ConditionExpression condition = new ConditionExpression();
    condition.AttributeName = "salesliteratureid";
    condition.Operator = ConditionOperator.Equal;
    condition.Values = new object[] { SalesLiteratureID.ToString() };
    //filter
    FilterExpression filter = new FilterExpression();
    filter.FilterOperator = LogicalOperator.And;
    filter.Conditions.Add(condition);
    // new query
    QueryExpression query = new QueryExpression();
    query.EntityName = EntityName.salesliteratureitem.ToString();
    query.ColumnSet = new AllColumns();
    query.Criteria = filter;
    // request object
    RetrieveMultipleRequest retrieve = new RetrieveMultipleRequest();
    retrieve.Query = query;
    // execute
    RetrieveMultipleResponse retrieved = (RetrieveMultipleResponse)service.Execute(retrieve);
    // do for each
    foreach (object o in retrieved.BusinessEntityCollection.BusinessEntities)
    {   // cast
        salesliteratureitem sli = (salesliteratureitem)o;
        // attach
        this.AttachSalesLiteratureItemToEmail(service, sli, EmailID, ref attachNo);
    }
}