Looking for feedback to idea about mac desktop app

Hey!

Some time ago I was overwhelmed with unread emails in my Gmail inbox. Mostly, they were newsletters, which I had no time to read. They piled up and I started to lose important emails in between them. At the time, there were more than 7000 unread emails (https://mailchaco.com/assets/images/image01.jpg?v57177303386151). I tried to clean it up manually but it was very boring and time-consuming.

I solved the problem with existing inbox cleaner in form of SaaS with a subscription plan (100$ per year for 5 mail accounts, cheapest service is about 60$ per year for 3 accounts). This was very strange for me because there was no need to have it on a server. I thought it is good opportunity to write the competing desktop app for inbox cleaning with one-time-payment differentiation.

I built the small prototype. It's very basic and just group emails by a sender with corresponding statistic and ability to move to trash whole group:

http://goo.gl/ocKof7

So, some questions:

• What do you think about this idea?
• Do you have this kind of problems with your emails?
• Did you use some online cleaners/unsubscribers like Mailstrom, Unenroll or CleanEmail?
• What should I do next? Just replicate competitors features or try to find early users with existing basic prototype? Should I charge them to validate idea or just reiterate on their feedback till value will be bigger.

Thanks for your feedback!