The ghost of Wingdings past is haunting you.
You're reading an email and suddenly there it is: A lonesome J dangling in its own nook of negative space.
Who are you? Why are you here? How did you find me?
This issue has actually been around since 2010, back when Microsoft released another version of Outlook.
If the sender sends a rich text document and/or HTML email, Microsoft subs in your typed emoticon with a Wingding. So if your computer doesn't support Wingdings, or just isn't feeling that emoticon, it comes up as a sad, eyeless little J. (And sad faces show up as Ls.)
Though he's flagged it with Microsoft several times to no avail, it's not a true bug, Pirillo writes, so long as you don't have Windows running and don't use HTML email. If you use Outlook, his post has a step-by-step guide to disabling these little monsters.
If you don't remember Wingdings, maybe this will jar your Microsoft memories:
Much wow, so visualization.
Microsoft / Via en.wikipedia.org
Microsoft needs to fix the problem, but they don't see it as a problem.
So, that's the problem.