my mail extension box is empty

I got an email today which didn't show the logo from the sender - instead it had a little question mark in the box where the logo should be. I remembered that I previously had this issue, so I googled and was reminded to go to my mail extensions to click something ...

When opening the extensions I found the box entirely empty as the attached picture shows.

I do not understand where my extensions in my mail program have gone - normally you would have the options to add or delete by using the little plus or minus sign ... but all of a sudden it is entirely empty - I just have an empty box with no options to do anything.

I have tried to google, but am only really able to find "restart your computer" and obviously I have tried - but that hasn't helped at all

anyone?