If you know how to use Inbox by Gmail, try Boxy and you won’t go back to whatever you were using (Spark, Airmail, Newton mail, Outlook, Mail.app). It takes the core functionality of Inbox by Gmail (snooze, done, bundles, email highlights for images and attachments, etc.) and puts it in a beautiful, native Mac client. Boxy is minimalist but powerful at the same time. The experience of using Boxy is fast and clean. It feels a lot more efficient than using the Gmail or Inbox web clients as you respond to emails and clear through your inbox. Using the native Boxy app is simply faster and smoother.
Although it requires a Gmail account, you can use it with any email provider by configuring Gmail’s Send Mail As setting for your non-Gmail accounts (Yahoo, Outlook, Office 365, whatever), giving you a beautiful, unified inbox.
The developers do a great job of rolling out regular updates that add new functionality and they squash bugs quickly. Keep in mind that some of the functionality comes from the Boxy developers (printing, attachment downloads) whereas other functions depend on Google’s development of Inbox (the way that signatures have been implemented). This means that client is constantly evolving.
Nothing helps you clear your inbox faster.