SQLBlackWhitelist using wildcards

Julian Field MailScanner at ecs.soton.ac.uk
Thu Feb 21 20:37:35 GMT 2008

Unfortunately you can't do that without slowing it down a lot. The 
SQLBlackWhiteList stuff, instead of allowing wildcards and hence having 
to check every entry in the list for every message, reduces the whole 
problem to a couple of hash table lookups which are very fast, as it 
knows that there aren't any wildcards.

If you allow the use of wildcards, every entry has to be matched against 
every address of every message. This is slow and is why MailScanner 
rulesets shouldn't ideally have more than several hundred (or maybe a 
thousand) entries. The SQL stuff does not allow wildcards much, with the 
result that it can just do table lookups to find if the address is 
listed or not. This is enormously faster than searching every entry of a 

The reason the SQL black+whitelist support is fast, not because of it 
being SQL (which actually makes it run slower) but because it doesn't 
support wildcards.

I hope that explains my design philosophy a bit for this feature.


William A. Knob wrote:
>       Hi all!
>    People, I want to use "wildcards" on my black/whitelist SQL tables 
> to use with Mailscanner... Anybody knows how can I do that? Or anyone 
> has made a modification on the "SQLBlackWhiteList.pm" script to do 
> that stuff?
>    Regards;


Julian Field MEng CITP CEng
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