I've bought Mailbird Pro several years ago, but I'm unable to use it anymore because I quit using Windows. I'm using Linux ubuntu nowadays which is much better, safe and faster than Windows, but there isn't a Linux version of Maibird unfortunately. I think you should take into consideration making a linux version of your software. I would love to have it on my Linux. There is nothing similar to it, nothing compares to it. Almost all the linux e-mail clients I've found out there are very limited and pretty old fashioned. The best one I've found is Mailspring, but Mailbird is way better!