This is due to HTML’s default operation when an image also has a link associated with it, and the “border width’ property of the email is unspecified.  

Follow these steps to remove the border:

  1. Login to your control panel and edit your email campaign
  2. Click the SOURCE icon to view the html code.

  3. Locate the HTML code for the image in question.

  4. Change the border width to 0 in the html code.

  5. Click the Source button.

  6. Save your email campaign and Exit.
  7. Send a test campaign to verify the blue border is gone.