Mailbutler is very useful for me. You managed to transplant most functions to Sonoma, but I can't get used to the new floating window, no matter how hard I try. ;) It is too independent of the main window for me. I think you have tried many different solutions, but for me PCalc's solution (https://pcalc.com) is much more natural. Maybe check it out if you haven't seen it yet. Thanks.