Download of Mimestream 1.4.1 for Mac was on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program lies within Communication Tools, more precisely E-mail. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. This Mac application is an intellectual property of Mimestream, LLC.
From the developer:
Mimestream is a native macOS e-mail client for Gmail. The application combines your favorite Gmail features with the power of a native macOS app so you can move through your e-mail effortlessly. Instead of using the IMAP protocol, Mimestream uses the Gmail API to enable an enhanced set of features that let you work with ease.
Your data and credentials are stored only on your device, and the app only makes direct connections to Gmail.
You may want to check out more Mac applications, such as SerialMailer, Mail Archiver X or MailMate, which might be related to Mimestream.