Starting this week, we are seeing horizontal lines, edge to edge, appearing between blocks in Outlook 2016 Windows app.
When we look in the raw source, there are empty <div></div> tags at those locations.
Hello @MCHT-Collier. I'm sorry that you are seeing these lines appear! This is something that has been noted by our engineers and is being researched further. We have mostly seen this happen on newer versions of Outlook and not on other email clients. The lines you are seeing are being pulled from the outer background color and changing the background color to the same white color should make these lines disappear when being viewed in Outlook.
Changing the background color isn't an acceptable solution, so I hope we'll be notified when the engineers resolve the problem.
I apologize this workaround may not be exactly what you're looking for. We have however added you to our queue to be notified when this experience is resolved.