Missive 10.64.1 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. We recommend checking the downloaded files with any free antivirus. Missive lies within Communication Tools, more precisely E-mail Tools. This program was originally produced by Missive.
From the developer:
Missive is a team inbox and chat tool that empowers teams to collaborate around email. It provides a modern interface where you can create your own team add team members to allow access to email inboxes. Each member can either me a "member" or "observer". You can discuss ideas with everyone, teams, or specific teammates using chat rooms. You can also do one-to-one chat with visitors on your website.
You may want to check out more software, such as Spam Monitor, SmartPOP2Exchange or SDP, which might be related to Missive.