I use the Mail ActOn plugin for Apple Mail. I haven't made the jump to Gmail because I spend so much time on planes, so I still use an offline email client.
Founder - Sendtask
1%Stacklist Startups Are Using Mail ActOn
Mail Act-On's powerful Keystroke rules and message filing interface gives you the ability to quickly take action on your email. Use Mail Act-On 3 to build sophisticated email workflows that eliminate repetitive, time consuming and error prone manual email organization.
Visit the website: https://smallcubed.com/mao/