What is this symbol? showing envelope with the number one on the envelope

[Windows Central Question]

envelope top left corner of screen with the number 1 sometimes 2 or 3. Also has two arrows pointing right at the side of the envelope.

 

[Laura Knotek]

Is it any of these? https://www.windowsphone.com/en-us/how-to/wp8/calling-and-messaging/what-do-the-icons-on-my-phone-mean

 

[RumoredNow]

That's how many new Gmail emails you have.