Short answer:
Outlook for Windows does not support valign reliably. Use a table cell with controlled height and an <hr> element as a workaround.
While web pages and emails both use HTML and CSS, email clients do not follow the same standards as modern browsers. Each email client uses its own rendering engine, which affects how HTML and CSS are supported.
This means that certain properties—such as valign—may not work as expected in some clients, especially Outlook for Windows.
Workaround for Outlook (Windows):
... <td colspan="3" valign="middle" width="300" height="2" style="width: 300px;font-size: 2px;line-height: 2px;"> <hr color="888888" size="2" width="100%"> </td> ...
This method uses a fixed-height table cell combined with an <hr> element to achieve consistent vertical alignment and spacing.
Result in Outlook (Windows):
