[syslog-ng] exemple for logging with a regexp

Hello, I'd like to ask you a queqtion about syslog-ng. I'd like to log for example, all mails from postfix in mail.log and for example all mails from courier imap to /var/log/imapd. I already manage to do that with syslog using facility like that: local0.* -/var/log/imapd.log mail.* -/var/log/mail.log But I'd like to add a regexp, so he didn't log all things. For example, for postfix, I'd like to add a blank line each time he find a line called "disconnect" or "removed". Is it possible to do that easyly with syslog-ng? Or I can also do that with my actual syslog? Because if I pass to syslog-ng instead of syslog, I'd like to keep my syslog config, except for those logs, that I want to filter with regexp. Thanks :-)