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On August 23, 2016 at 6:57 PM Sam<sr42354@gmail.com> wrote:

Hello,

Sometime when we receive a spam or virus that is detected as it, mailer daemon send a reply to the sender to inform that the message is a spam or content viruses.

The problem is that the sender of the spam as something like voicemail@ourdomain.fr ( the user voicemail doesn't exist in our database )

And sometimes dovecot create the directory and store the reply 's mail...

If I understand your question correctly, you are sometimes sending an after-the-fact bounce message based upon the return-path in at least some situations where you detect a spam or virus (as opposed to responding with an error code response during the SMTP session)?

If my understanding is correct, you should never ever ever ever ever ever ever send those sort of NDR's. Please google "backscatter".