Interesting. I wrote something very much like this for internal use at my company. Basically we have a lot of legacy alerts and messages and reports that are "dumb" (i.e. if a cron job runs once a minute to detect problems within one minute it will keep on mailing until it's fixed because it has no state) so the new mail system sits in front of it all and says, hmm, saw that a minute ago, won't bother the humans with it again, they're probably busy actually fixing it.

It's not, and never will be, a general purpose mail server - old-fashioned SMTP servers have their flaws but it's as good as it gets if you want mail that can reach anyone, anywhere.