Sysop can set the number of days-worth of new messages that new users will
see in their first new-message scan (the default is 0, no new messages).
This does lengthen the amount of time that the first "Loading message pointers"
is displayed (it has to go and open all the message bases), but at least new
users are no longer bombarded with thousands of very old messages when they
answer "Yes" to the "Scan for New Messages" prompt. This setting is in
SCFG->System->New User Values->Days of New Messages. Set it to some really
high number (maximum of 9999) if you want the old behavior.