Readdle's Spark[1] has been my Inbox replacement since Google killed it. It has pin/snooze functionality and a similar concept of grouping emails by category and letting you easily mass mark-as-read. Plus, you can connect multiple email accounts rather than just being limited to your Gmail account. It's also nice because you can have a "team"; my wife and I use it to share important messages and help each other draft or review emails. They have really nice apps for Mac and iOS, too.
[1]: https://sparkmailapp.com/