Disabling email notifications from Android Hangouts app.
I figured this out myself and I'm posting the instructions below in case others have trouble as well.


Login to your Google Voice account. 
Click on the cog near the top-right of your screen then select "Settings" from the drop-down.
Click on the "Voicemail &amp; Text" tab.
Under the "Text Forwarding" header, uncheck "Forward text messages to my email:"
Click on "Save Changes."