Yeah, I also used to run qmail and first knew of djb as the apparently only person capable of implementing network protocols in C without any exploitable bugs :)

But, he was actually doing historically important cryptography work even back then: https://en.wikipedia.org/wiki/Bernstein_v._United_States (and since has gone on to co-invent several cryptographic primitives which are now ubiquitous internet standards).

His web site is https://cr.yp.to which is a cool name ;).