As I understand it, the idea of Missive is to replace a traditional help desk system with direct email communication between customers and support staff into shared inboxes. This theoretically eliminates the redundancy of support staff having to use both a regular email client to communicate internally and also respond to customer issues via a web-based support portal.
I like this approach, because I like anything that eliminates redundancies and increases efficiency. However, I also feel that many customers would prefer to use a traditional help desk, where they can view all their tickets and respond directly, rather than via email. Personally, I often feel uncomfortable when a company tells me to email support, rather than providing a help desk, because email is so unreliable. You never know for sure if your email has been received or read and there's no way to view the status of your tickets or view old tickets. I know Missive provides read tracking on our end, but customers are on their own.
For these reasons, I'm wondering if you'd considered creating a a web UI for customers that would emulate many of the features of a traditional help desk? You could create a special category of email conversations that are tagged as support tickets. For these conversations, Missive would automatically create a ticket for each conversation and would include a link in each email reply that would allow the customer to view/update the ticket online. Customers could open new tickets in the help desk or we could manually tag any email as a ticket, or use rules to convert emails into tickets.
This way, we'd have the best of both worlds. From the customer's perspective, it would function like a traditional help desk. On our end, we'd use Missive just like we do now, except we'd be able to view create and view "tickets" which are really just conversations that have been tagged as such. I may be oversimplifying a bit; obviously you'd have to assign ticket numbers, statuses, etc.... but I think most of the elements are already in place. We just need the customer-facing web UI.