I would love to be able to sort my inbox by From: I find this helpful on occasion when cleaning up my inbox. I also find the same helpful in my sent box to be able to sort by To:

Add calendar into Missive. For meetings, tasks, invites, etc.

What will make your platform perfect solution is voice channel which I think is really missed. An option to use twilio voice number just like the use of twilio online chat api. Option to set IVR menu, queues, group calls, customer contact popup upon call, click to call, custom greeting, set hold music, simultaneously ringing or ring by order groups, call back, call transfer and more... Sip phones integration so when customer calls the phone will ring and the customer details will pop up on agent screen, when click to call the call will be made via the sip phone . Of course every call will be saved as conversation and the agent will be able to write private notes and the call record will be available there. It’s a big project but I think that this is really missed in your system. You don’t offer any voice channel. I will be really happy to hear what do you think about it.

A "Send & Snooze" option next to "Send & Archive". I know there is already the ability to click the snooze button, set a time for snooze, then click the send button, but this would be a more elegant solution that would save time and clicks. If it could remember the last time you snoozed for (say I just snoozed an email til 8am next monday morning), and automatically enter that same snooze duration unless told otherwise, that would be even better.

When agent sends a message out of the 24 hour time which is not a template message the message will not be delivered. Like in Facebook integration it will be really helpful if the system will show red error which says this happens because of WhatsApp template message policy. Add option to send pro-active WhatsApp template message (and actually also sms) when creating new conversation and not only emails. Add WhatsApp audio message support so agent can hear audio messages from missive interface WhatsApp conversations does not appear under contact last conversation

The ability swipe/pull down inside an inbox to sync. Although the app may be push, I want to ability (even if just perceived) to sync myself to it feels the most up to date in that moment.

I would love a 'solo' plan that is somewhere between the two paid plans you already have, which allows for solo usage only, thus fitting freelancers like me best. I am a bit turned away by the price of the unlimited plan and wouldn't need the team features at all, but would love to see all my e-mail instead of only recent mail.

I'm drafting a new email and would love it if I could press cmd + f to search the entire thread for a specific string. This is in the OS X client.

Active users could translate UI if you just include some localization file support in app.

I'd like to be able to see when a recipient clicks links that are contained in the body of an email to them. (Similar to open tracking.)