Log in screen shows envelope & a number by it, why??

[learninmypc]

NO UN opened emails in any of my addy's yet as my Acer desktop gets to that log in screen, it shows an envelope & this time it shows 6. Why? How do I stop it,if I can. W10 Acer all in one.

 

[learninmypc]

I don't have/use skype on my pc https://answers.microsoft.com/en-us...-10-lock/6522dbac-0fd7-4a48-9a4a-79cf330d6aec