[pengo]

I've used Thunderbird on my desktops since it was launched and, despite its shortcomings, find it works well for my multiple accounts. I host my own calendar and contacts services and these integrate well too. The current desktops I use email on are all Linux Mint; on the rare occasions I need to access mail on other machines I log into one of my server's webmail clients (usually Squirrel).

Mobile? I'm still running a Blackberry Z30, hopefully replacing it with a Librem 5 later this year. I use the default Blackberry app and it works superbly with my multiple accounts (I'll miss it).