What is this interface icon mean in Gmail?

Question

What does the question mark icon next to the sender's email in Gmail stand for?

I have been able to deduct what the X and the exclamation mark stand for but can't figure it out with the question mark.

Answer 1

This is a 2016 Gmail feature. It indicates that Gmail can't confirm the sender's identity. In other words, Gmail is telling you that the email could be from a different sender than it says it's from.

Here is the Google support article on the feature.

Here is the original announcement.