Postfix provides many tools to simplify problem solving. While implementing new features in your Postfix mail system, do it step by step. The more unsure you are in what you are doing, the smaller should be the steps that you take. If you run into problems, you will discover them early and it will be easier to figure out what went wrong. This is especially true when implementing complex lookup tables using MySQL databases.
Note
If you are even slightly uncomfortable with complex lookup tables, never introduce a new feature and a complex lookup table configuration at the same time. If something breaks, you will have much more trouble figuring out where to start.
When trying out new configurations, it does not hurt to be on the cautious side until the configuration is fully tested. By setting the following feature all permanent errors will be turned into temporary errors:
soft_bounce = yes
This means the transmission of any messages rejected by your server will...