An email template that uses anchor tags (jump links) to different areas of the message inserts the BASE tag https://system.netsuite.com/ to all relative anchors such as <a href="#top">Back to top</a>.
i.e. The email message includes a "Back to Top of Page" link and clicking it should return the user to the top of the page. This looks like:
<a href="#top">Back to top</a>
The "Back to top" link now has a URL of https://system.netsuite.com/#top. The link opens a new page when clicked from within Outlook.
To make sure https://system.netsuite.com/ isn't appended to any of the anchor tags, open the template file in Mircrosoft FrontPage and configure the anchor tag urls and copy/paste the html into the template record in NetSuite. This method ensures no additional html is added to the template and anchor links work as expected.