Streak is a CRM (client relationship manager) in your inbox. Organize emails & much more with streak, which is a free app extension.
WiseStamp is a free plugin for Gmail
How it helps: make a professional email signature, including links to social accounts, for free!
Boomerang is a great app for people with clients & have set hours. You can write an email and have it send when it makes most sense for you.
Need to check emails but don't want to have to keep it open in your browser? Download Kiwi for Gmail! It turns your email into a separate app on your computer.
In order to find your client emails, make sure to first get rid of all the spam. Unroll.me is a service that allows you to "roll up" or curate your emails into one, unsubscribe or keep in inbox.