This just isn't feasible for me from a usability perspective. Private email is with Fastmail, but work email is something else entirely. Both have good webmails

This just isn't feasible for me from a usability perspective. Private email is with Fastmail, but work email is something else entirely. Both have good webmails, but vastly different UX. By using Thunderbird I can get the same UI/UX for all the different email providers. If I only had Fastmail, I'd also be OK with just using their webmail, it's excellent.