Yahoo mail extreme memory consumption on Sierra

Hello MirajKing,
Thank you for using Apple Support Communities. It's my understanding Yahoo Mail is using an unexpected amount of memory after updating so Sierra. I can surely see how this would be concerning. I am happy to help.
If you haven't done so already, I recommend restarting your MacBook Pro. This can resolve many unexpected behaviors and activity. If you're using Yahoo Mail in Safari, clearing your browsing history can help clear some of the memory used. Here's some additional information on how to clear the history and what's removed.

Choose History > Clear History, click the pop-up menu, then choose how far back you want your browsing history cleared.

When you clear your history, Safari removes data it saves as a result of your browsing, including:

• History of webpages you visited

• The back and forward list for open webpages

• Top Sites that aren’t marked as permanent

• Frequently visited site list

• Recent searches

• Icons for open webpages

• Snapshots saved for open webpages

• List of items you downloaded (downloaded files aren’t removed)

• Websites added for Quick Website Search

• Websites that asked to use your location

• Websites that asked to send you notifications

• Websites with plug-in content you started by clicking a Safari Power Saver notice

• Responses to requests to let websites use WebGL

Clear your browsing history - Safari Help

Have a great day!