by rob » Tue Mar 04, 2008 4:56 pm
This depends on your settings. Basically in a normal setup where relaying access is only permitted to verified users (either by authentcation or IP, which is controlled by the relaying access settings in the SMTP service), trying to deliver a mail to a non existant user should result in a refusel with the error message "Relaying not permitted." This happens at the SMTP before content filtering can have any effect. However, if the client which is delivering these mails is authenticated (either by your settings allow relaying access to all or by the mails being delivered by authenticated users), then your content filtering rules will indeed pick htese mails up. What I can recommend is ensure your server is setup so users require SMTP authetncation to send mails to external accounts, if this is already setup then one of your users may be abusing your system by trying to deliver SPAM (I would recommend tracing the mails by examinig the headers, obtainig the sending IP, then search for this IP in the SMTP logs).