Why does my HTC One M8 give me a login failure message?

[AC Question]

htc onem8 login failure message

My HTC m8 keeps showing a Login failure message for my Gmail. It still receives my mail, but I can't send mail. Anyone know how to fix it please, it's so frustrating??!!

 

[B. Diddy]

Re: htc onem8 login failure message

Welcome to Android Central! Are you using the Gmail app or the stock Email app?