Plesk silently discard bounce message?

[asfik]

Hello,

I just realized if I sent email from webmail to invalid mailbox, Plesk's Postfix local transport will discard the message without sending bounce message. Here for example:

Aug 23 22:47:00 server1 postfix/pickup[24781]: 9008C9F21760: uid=48 from=<user1@cooldomain.tld>
Aug 23 22:47:00 server1 postfix/cleanup[25361]: 9008C9F21760: message-id=<20130823224700.107441ahiqwrw90k@webmail.cooldomain.tld>
Aug 23 22:47:00 server1 postfix/qmgr[17270]: 9008C9F21760: from=<user1@cooldomain.tld>, size=719, nrcpt=1 (queue active)
Aug 23 22:47:00 server1 postfix-local[25364]: postfix-local: from=user1@cooldomain.tld, to=user2@cooldomain.tld, dirname=/var/qmail/mailnames
Aug 23 22:47:00 server1 postfix-local[25364]: cannot chdir to mailname dir user2: No such file or directory
Aug 23 22:47:00 server1 postfix-local[25364]: Unknown user: user2@cooldomain.tld
Aug 23 22:47:00 server1 postfix/pipe[25363]: 9008C9F21760: to=<user2@cooldomain.tld>, relay=plesk_virtual, delay=0.06, delays=0.04/0.01/0/0.01, dsn=2.0.0, status=sent (delivered via plesk_virtual service)
Aug 23 22:47:00 server1 postfix/qmgr[17270]: 9008C9F21760: removed

This is not very good since sender doesn't know if the email was never goes to right destination. Please let me know if you have any comments. Thanks.