Randall Stross wrote an article in the New York Times on how to handle email. It also contains a message for agents, producers and others who fail to even acknowledge letters or emails. Here's an excerpt:
"We all can learn from H. L. Mencken (1880-1956), the journalist and essayist, who was another member of the Hundred Thousand Letters Club, yet unlike Edison, corresponded without an amanuensis. His letters were exceptional not only in quantity, but in quality: witty gems that the recipients treasured.
"...In his correspondence, Mencken adhered to the most basic of social principles: reciprocity. If someone wrote to him, he believed writing back was, in his words, “only decent politeness.” He reasoned that if it were he who had initiated correspondence, he would expect the same courtesy. 'If I write to a man on any proper business and he fails to answer me at once, I set him down as a boor and an ass.' "
Stoss adds: "Today’s advice from time-management specialists, to keep our e-mail software off, except for twice-a-day checks, replicates the cadence of twice-a-day postal deliveries in Mencken’s time."