I fully believe that people should be wary of "just rewrite it mentality". However, in this case, when we've had a mostly-dormant Thunderbird for a long time, based on what is now an outmoded development toolkit (the outmoding of which supposedly had a non-trivial amount to do with security) backed by a very complex and large upstream codebase, which is itself in the process of being abandoned for next-gen solutions, is it really wiser to resurrect the old code?
I've used Thunderbird off and on since it was announced and I know that it has many advanced features. It's no slouch and I deeply respect that there's still a local mail and news client that somewhat works and sometimes gets a little bit of TLC. But the ecosystem is in shambles, and this is only going to get worse as Firefox diverges.
It would obviously take time for a serious revamp to reach parity, but Thunderbird needs a total skeletal reconstruction to pull it off life support and get people excited again. This is just upping the cholesterol meds.
All the other "client-side email software" applications in recent memory have been Electron apps. Surely Mozilla can do us one better, and build a revitalized Thunderbird with staying power on an appropriate modern stack? This seems like a great pilot project for a serious Rust-based desktop toolkit.