redirect incoming mail to script

[santo]

I want to integrate zimbra with a project management tool which can accept mails to put them in a queue so that users can attach them to tasks.

For this I need to be able to redirect incoming mail for a specific user to a perl script, which will then add the message to a queue in the project management tool.

On a default system, this can be done by adding an alias for this account like this:

opt: "| /usr/bin/perl /var/www/opt/include/mail_retrieve.pl"

Unfortunately, this doesn't seem to work.
As seen in the logs, zimbra simply accepts the mail and puts it in the inbox for that user:

Mar 16 12:45:24 server02 postfix/smtpd[31091]: connect from server01.mydomain.tld[192.168.1.201]
Mar 16 12:45:24 server02 postfix/smtpd[31091]: DFCB5B739D: client=server01.mydomain.tld[192.168.1.201]
Mar 16 12:45:24 server02 postfix/cleanup[31092]: DFCB5B739D: message-id=<WorldClient-F200703161245.AA45030014@mydomain.tld>
Mar 16 12:45:24 server02 postfix/cleanup[31092]: DFCB5B739D: resent-message-id=<20070316114524.DFCB5B739D@server02.mydomain.tld>
Mar 16 12:45:24 server02 postfix/qmgr[28442]: DFCB5B739D: from=<testuser@mydomain.tld>, size=2361, nrcpt=1 (queue active)
Mar 16 12:45:24 server02 postfix/smtpd[31091]: disconnect from server01.mydomain.tld[192.168.1.201]
Mar 16 12:45:25 server02 postfix/smtpd[31096]: connect from localhost[127.0.0.1]
Mar 16 12:45:25 server02 postfix/smtpd[31096]: 5275AB73A1: client=localhost[127.0.0.1]
Mar 16 12:45:25 server02 postfix/cleanup[31092]: 5275AB73A1: message-id=<WorldClient-F200703161245.AA45030014@mydomain.tld>
Mar 16 12:45:25 server02 postfix/cleanup[31092]: 5275AB73A1: resent-message-id=<20070316114524.DFCB5B739D@server02.mydomain.tld>
Mar 16 12:45:25 server02 postfix/qmgr[28442]: 5275AB73A1: from=<testuser@mydomain.tld>, size=2993, nrcpt=1 (queue active)
Mar 16 12:45:25 server02 postfix/smtpd[31096]: disconnect from localhost[127.0.0.1]
Mar 16 12:45:25 server02 postfix/smtp[31093]: DFCB5B739D: to=<opt@mydomain.tld>, relay=127.0.0.1[127.0.0.1], delay=1, status=sent (250 2.6.0 Ok, id=28401-01, from MTA([127.0.0.1]:10025): 250 Ok: queued as 5275AB73A1)
Mar 16 12:45:25 server02 postfix/qmgr[28442]: DFCB5B739D: removed
Mar 16 12:45:25 server02 postfix/lmtp[31097]: 5275AB73A1: to=<opt@mydomain.tld>, relay=server02.mydomain.tld[192.168.1.202], delay=0, status=sent (250 2.1.5 OK)

So my question: How can I configure an alias in Zimbra which will redirect incoming mails to a script ?