I just started to listen to the episode.
I used to use #Thunderbird, what annoyed me (besides the 1 GB of stuff it stored in .thunderbird instead of under .local/share) was that it brought notifications of calendar items and tasks BEFORE it synced them, so after going home from work, I'd be blasted with all my "missed work appointments" that I actually handled on my phone and got synced to Nextcloud.
So for e-mails I went back to pinned tabs in FF, and calendar I went CLI.