i don't see anything in the postfix readme's about setting it on a per-user basis (or other searches / co-workers / etc).
the best 'quote' i can find is from the
http://www.postfix.org/TUNING_README.html :
The smtpd_recipient_limit parameter (default: 1000) controls how many recipients the Postfix smtpd(8) server will take per delivery. The default limit is
more than any reasonable SMTP client would send. The limit exists to protect the local mail system against a run-away client.
so, having said that, are there people on your system that send to more than 100 at once? is there one in particular that is sending too much so you're trying to block their access?