Thank you to all who responded to my question, both on and off the list.

Several respondents suggested locking the lists to prevent subscribers from
leaving. This would be effective, however, it is neither politically acceptable
nor fool-proof.

Some respondents suggesting refreshing the subscriber lists periodically, using
data from outside sources. Thousands of course-related lists are refreshed
nightly. The all-faculty list and its sub-lists are refreshed weekly. The
all-staff and all-student lists are refreshed by the respective list owners, at
their discretion.

--
Paul Russell
Senior Systems Administrator
University of Notre Dame