Consideration:code of custom attribute is custom
Note: Please do not edit core files, Copy below files to your Theme
First we need to add a column to template:
file path:app\design\frontend\rwd\default\template\email\order\items.phtml
add below code before Qty th
<th class="cell-name align-center">
<?php echo $this->__('Custom'); ?>
</th>
Now we need to get value of custom attribute.file that is responsible for getting all attribute values is:
app\design\frontend\rwd\default\template\email\order\items\order\default.phtml
In above file when you log $_item, it will default not having value of custom attribute.So what we need is to load product and get value of product custom attribute. for that you need to add below code before Qty td:
<?php $_product = Mage::getModel('catalog/product')->loadByAttribute('sku',$_item->getSku()); ?>
//load product by sku
<td class="cell-content align-center"><?php echo $_product->getCustom(); ?></td>
//add td column with attribute value
Result: