When you receive a new e-mail and that e-mail is not on your "Safe Senders List" in Outlook, images in an HTML email will not be visible. This is by default that HTML images are turned off and not downloaded. To get them to appear you would then right click and choose junk.. “Never Block Sender” or “Never Block Sender’s Domain” or “Never Block this Group or Mailing List”. Once you do one of these three, it adds that type of email to the Junk Email Safe Senders List.
As a result every time you get a new email from that person, domain or mailing list, all the images will be downloaded, letting you view the email in its full glory.
Flash forward to a machine wipe, starting from scratch.
If you have ever had to reinstall office on a machine, from scratch, you know that by default on a clean machine, there is no data on your safe senders. There is an option in Outlook that lets you import and export this list that many may not be aware of...