Wait, are you saying that qmail was written as a replacement for PMDF? Or that you used qmail as your replacement for PMDF?
"In 1999 PMDF was translated from Pascal to C. The C version of PMDF became the basis of the Sun Java System Messaging Server of Sun Microsystems"
I wouldn't bet that (the C version of) PMDF was reimplemented in Java just because the name contained Java. I seem to recall Sun putting Java in the name of many products at the time.