Hi Ellie,
If your wanting the border to follow the height of the text only then you can slip your border style in the nested table role="presentation"
<!-- Column : END -->
<!-- Column : BEGIN -->
<td class="stack-column" valign="top" align="center">
<table role="presentation" cellspacing="0" cellpadding="0" border="0" width="330" style="margin: auto; border-left: 2px solid blue;">
Scroll to the right to see where I added it to your inline styles