[Dovecot] How to copy Spammail for learning out of Postfix and Dovecot (vmail)

Hi!

I am using Postfix 2.3.8 and Dovecot 1.0.rc15. Virtual Domains and Mailboxes are configured.

I tried to copy spammy Mail with Procmail, but Procmail only sees local mails. How to configure it to get a copy of spammy mails in a mbox or mail-dir?