What is a question about this article? If the question is unanswerable, say "unanswerable".

Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required many computer systems to be upgraded, with the greatest impact on email and calendaring programs; the upgrades consumed a significant effort by corporate information technologists.

In addition to calendaring programs, what kind of programs were most impacted by the changes?
email