A very interesting video about the Thunderbird Project successful donation process and how KDE can improve them by following their step.
Most operating systems, excluding Windows, are shipping with decent native and fast email client.
Even Windows ships with one (“Mail”). I don’t have any real experience using it (on my Windows work laptop I have Outlook, and on everything else I use Thunderbird), but it looks fine to me.
I have no idea what the pricing scheme is for Outlook these days, but Outlook does remain genuinely excellent too.