One of the unknowns of emailing is the time it will take the receiver to form and post a reply. Response times vary considerably, and the chronemics of email are an important non-verbal cue which can convey meaning as well as influence interactional coherence. While privacy and technical challenges have so far limited quantitative assessment of responsiveness chronemics, an opportunity became available with the recent release into the public domain of an unprecedentedly large corporate collection of private email messages. An analysis of over 16,000 responses extracted from a large database of email messages created by Enron employees was performed. Responsiveness profiles of individual users and of all users are described, and their aggregate temporal distribution is evaluated. The generalizability of these findings as well as their implication to current theory on email response times is discussed.