I haven't used Thunderbird in a long time, but regularly used Outlook with multi-gigabye .pst files. Surely sqlite on an SSD would be up to the task of handling at least million emails of average size.
I did an internship in IT 20 years ago where we were building/maintaining desktops and other general helpdesk type stuff. I'm pretty sure I remember us having a handful of users with multi-gig pst files, running on 2005 hardware.
> Outlook with multi-gigabye .pst files
What has been your experience? Mine in trying to use and support it is that Outlook is an Exchange client; PSTs are hacks to meet demand, though they work well enough in limited circumstances. Especially PSTs over a LAN connection are a disaster.