I got close to a thousand email daily. Is there any nice email searching (supporting regex, checking multiple fields, etc.) and sorting plugin I can use with Thunderbird?
I sometimes use Mutt but it's not available on a few computers I use.
In my opinion it is the wrong approach to do have the sorting done by the client. Ideally, mail should be sorted by the server when it arrives (i.e. not be placed in your inbox but elsewhere).
A setup that does very well performing that task is the dovecot MDA with sieve support - sieve is a protocol that allows every user to write a rules file that is then used by the server to sort the mail on arrival. Clients can contact the sieve service to edit the rules. There exists a Thunderbird Plugin here, RoundCube webmail also has support for it: