Preview PDF and Word, Excel, Powerpoint documents
I love how Gmail and other web applications allow you to click an attachment to preview WITHOUT downloading the document. This is particularly useful for Microsoft documents, since the Microsoft applications take forever to open.
Calendar invites (.ics files) handling
Handle .ics event invitations and responses with shortcut buttons (Accept, Refuse, etc).
Highlight terms in search results
The search function returns a list of conversations and emails containing the query but it doesn't highlight them inside the conversation. Conversations can be very long may not even load the portion containing the search terms.
It would be great to be able to drag and drop emails in a kanban view like cards in trello to create a mix between to-do and emails
Automatic follow up if no reply
This could be a killer feature for Missive: https://www.ifnoreply.com/ :)
Shared signatures with dynamic variables
Imagine being able to administer a whole company's signatures from within Missive. Where you could create several different signature designs by choosing and editing templates, or creating your own, and Missive would automatically insert the names, phone numbers, etc of the users with the assigned signatures. You could also add marketing graphic below the signatures and assign it automatically to specific departments within the company. https://www.letsignit.io/ is on to something here.
Family plan (at a cheaper price)
I use Missive all day and it would be lovely if I could comment on emails with my wife and use the teams for managing our family. I couldn't justify the cost for personal use. Something as simple as requiring us to be a part of a Productive level organization, we could get a bonus organization with a 2-member limit for family use for free/cheap.
View all attachments in the conversation / email thread
Front has a similar feature when you click on the information icon. It lets you preview all attachments in the email thread and download them instead of searching for them through emails. It is very useful as we send clients a lot of PDF documents and it would be great to se them all in one place.