What is the "N..." on the Form submissions list mean?

When looking at the submissions for the various forms, there is one that has an envelope in the "N..." column, but I can't for the life of me figure out what that means.  It's directly under "Download as:"

Thank you!

Let me please inform you, than this is a 'New' submission column. You can click on the small letter icons to mark your submissions as the 'New' ones.

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