>>851
-- main.cf
transport_maps = regexp:/etc/postfix/transport.regexp

-- transport.regexp
/^ABCDE@example\.jp$/idiscard:
/^abcde@example\.jp$/ierror:

% echo test | mail -s test ABCDE@example.jp

Aug 13 13:40:07 <mail.info> hoge postfix/discard[14811]: BECD3211E: to=<ABCDE@example.jp>, relay=none, delay=0.94, delays=0.87/0.07/0/0, dsn=2.0.0, status=sent (g.maya.st)
Aug 13 13:45:53 <mail.info> hoge postfix/error[14888]: 182D3211E: to=<abcde@example.jp>, relay=none, delay=1.5, delays=0.7/0.27/0/0.58, dsn=5.0.0, status=bounced (Address is undeliverable)

大文字小文字の違いに応じてちゃんと discard/error が使いわけられてますが。