Qmail is far from flawless. It could be better if patches were allowed, but no, that's forbidden.
As much as DJB is a talented programmer, his attitude towards outside contributions comes across as extremely hostile.
I can't take any of the DJB projects seriously because they're always in a state of permanent abandonment and maintainers are impossible to find. They serve as art pieces more than practical, useful software.
He's certainly from the old school of development where tight control over your software ensures it's not exposed to risk from external developers, and of course he's entitled to do that. The consequence is that severely limits how this software can be used.