The Microsoft account email ID is displayed by default in the login screen. To improve your privacy and security, you can hide your MSA email address from the login screen. Here is how to do that in Windows 10 v1607 (Anniversary Update).
Remove Email Address from Windows 10 Login Screen
Open Settings (WinKey + i), click Accounts, Sign-in Options.
Under Privacy, turn off the setting “Show account details (e.g. email address) on sign-in screen.”
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Ramesh Srinivasan founded Winhelponline.com back in 2005. He is passionate about Microsoft technologies and he has been a Microsoft Most Valuable Professional (MVP) for 10 consecutive years from 2003 to 2012.