Five years after the first line of code, Stalwart v1.0 is here: the first stable release, with a finalised database schema, months of profiling and stress testing, a rewritten search engine, and benchmark results that put it ahead of Postfix and Dovecot in 35 of 38 tests.
Qmail was fast. Exim is plenty fast. Like how fast does it need to be? I admire the ambition but make Linux faster, o something.