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qmail-sql 0.22

Hi all,

Qmail-SQL 0.22 is now available. If you were already using 0.22pre6,
there's no need to upgrade since nothing changed. 

The main new feature is the ability to check whether a user exists or not 
_before_ accepting the mail: at smtp-level. This protects against a specific 
type of spam-attack. Suppose you have a domain 'foo.org'. A spammer chooses 
the non-existing address bar@xxxxxxx to send the junk. Complaints and bounces 
go to bar@xxxxxxxx With the new patch, the server immediately rejects this 
mails, which should save resources on your server and network.

It also protects your postmaster from getting too much bounces about spam
sent to non-existant users.

Why 'too much' ? Because it doesn't stop all mail to non-existant users. 
Suppose mail arrives for foo-test. There's no way for qmail-smtpd to check
whether ~foo/.qmail-test exists. So it will accept everything for foo-*.
Using the dotqmails-table it's possible to create these aliases without
.qmail-files but i didn't yet decide whether qmail-smtpd should disregard
the posibility of .qmail-files or not. Any remarks are appreciated !

Note that this feature won't work well if you enabled the 'localtable'. This
option is likely to disappear in a future release.

Other changes include:
- improved quota calculation: solves the 'process_cannot_open_more_files'
- quota are only calculated if necessary
- fixed segfault with qmail-getpw when invoked incorrectly
- small code-cleanup