Postfix header checks

Hi, I'm getting spam messages with a empty subject line. I would like to have Postfix to refuse these, so I need to have a line in my header-checks list. I'm new to this (I copied a list from http://www.securitysage.com/files/header_checks.short) and I'm unsure how to write such a line. Would '/^Subject:!.+/ REJECT ...' do the job ? I think it means 'Subject:' followed by 'not (more than zero characters)'. B.T.W. is it possible to modify the header checks 'on-the-fly', i.e. without restarting Postfix ? Maybe with MySQL ? Another though : should Amavis/Spamassassin do this ? TIA. -- Met vriendelijke groeten, Koenraad Lelong R&D Manager ACE electronics n.v.