I timed a test of deleting 5000 (well, really 4900) records using REGISTER
... OFF, and found that Listserv does ~200 names per minute (on our site;
ymmv). So deleting 275000 names will take about 23 hours. I can break this
up into smaller chunks, but regardless the web interface is
inaccessible/unusuable when one of these things is running. Click on the
web interface, nothing happens for however long- wonderful customer
service. I can do it several early mornings, but while that removes most
of the impact from SU customers (although a university never really
sleeps), it's not good for international customers. I can't even
realistically announce outages, because we can't email 120k subscribers
over 1900 lists (yes, we can let list owners know). And regardless of
which way I go, it's a pain to manage in chunks.

Probably I should have done this long ago, but I didn't even realize it
was a (potential) problem.

- Listserv List Manager
Listserv webpage: http://listserv.syr.edu
Web access to List Archives, Manuals, and List Management for Owners.