@gwmngilfen Glad you like it! And thanks for asking!
It's a tricky question; we are lacking a venue for general discussions. Github issues and IRC are all we've got. The problem of course is that I mostly want issues to be actual issues, and IRC is too ephemeral.
If it's more impressions and not actual bugs, maybe just send me an e-mail at [email protected]? Or if you have a blog, more people writing about Mailpile is never a bad thing...