After looking at the Gmail Advanced Search Operators, I found a really cool hidden feature with “Stars”. Gmail Stars let you mark an email as different category to signify something important to you. To get started with Stars, head to Gmail’s settings and in the General section, move down to the “stars” section.
You can now toggle between them by clicking the star button.
From there, you can search for different stars with some advanced Gmail Searches, which is pretty sweet.
This makes your life easier. Trying to juggle multiple clients or projects? Designate them with different star colors!