ONLamp.com: Troubleshooting with Postfix Logs [Jan. 22, 2004]: "Use the soft_bounce Parameter for Testing Changes

When trying out a configuration change you're not sure about, you can enable soft_bounce, so that mail that would bounce is kept in the queue and can still be delivered once the problem is corrected. In your main.cf file, simply add the following:

soft_bounce = yes"