I'm sorry but I'm going to provide negative feedback here which I feel kind of guilty about because clearly a lot of work has gone into building this.

The first thing I didn't like is that from the photos on your website it didn't look like it has a mac-like UI.

I downloaded it anyway to have a look and then noticed the application is 460 megabytes. Mail.app and MailMate are each only 28mb. I'm guessing a web based technology was used to build the app which also means that it's going to run really slow on one of my older Macs.

Finally when I launched the app the first thing it did before even opening a window was ask me for my admin password in order to make a modification to my keychain. I clicked cancel at that point and the program didn't open.