Comcast (aka "Xfinity") provides Norton Security Suite to their customers for free. That makes sense. It's a win/win for everybody all around. Part of that package is an anti-spam filter.
Lately I've discovered email from Xfinity itself (legit, I checked) misfiled by Norton to my "Norton AntiSpam Folder" with no apparent way to correct the (metamistake. ← © Jimaz, 2016)
This is a great illustration of how organizations (or partnerships thereof) can become so obese that the left hand doesn't know what the right hand is doing.