My feeling is that, where someone thinks a response might be of interest to a
number of others on the list, he/she should post it to the list. However, if
there's something I think is likely to interest only old John in Albuquerque,
old Gail in Stockholm or old Tim in Melbourne, it should be sent directly to
the individual concerned. There are times, however, where one doesn't know a
colleague's email address and has to beg the indulgence of others to send
something through the list. There are also times when one makes a boo-boo and
send an obviously private bit of  correspondence to the whole (expletive
deleted) list (see, inter alia, "When Kersti Met Harry" [1995]) and other
MUSEUM-L classics of the genre.

Harry Needham
Canadian War Museum