Comparing 2 different email lists from 2 different worksheets

So im relatively new to Excel, but know the basics. Im trying to compare 1 list of around 500,000 emails in Column A to another list of Emails (around 600,000) in a different worksheet in Column K.
The point being, Im trying to see which emails are present in both worksheets as one worksheet represents a client list, and the other is a global list of emails subscribed to a newsletter.
So im trying to see what emails are in the global list that are in the client list.

Does anyone know how to do this or is more explanation required?