[Qmail-scanner-general] prevent spam to mismatch address

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I have qmail+vpopmail
Users recieve mails that dont address them ("To" field contain different
emails from local server)
There are no any forwarders and maillist
I installed qmail-scanner with SpamAssassin and there was no result
Can qmail-scanner prevent this or is there any patch?
I think this is qmail bug is it?

Thank you for help