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Blocking spoofed emails from own domain


We are running Exchange 2003 SP2 on Windows 2000 Servers. One front end, one backend. We also have a mail gateway (where our MX record points to) that is responsible for anti-virus/anti-spam running Trend Micro IMSS Our domain is domain1.co.uk.

Occasionally, we occasionally get spoofed emails from our own domain, e.g. mails from dsfsfsf@domain1.co.uk, being sent to users. The strange thing is that there is no 'to' recipient on these emails, that field is blank, but it still gets delivered to the odd user. I traced the source IP address of these mails, and they are originating elsewhere.

My question is, is there an option in Exchange to block incoming external mail where my domain is the sender? And does anyone know why emails with no 'to' field as being delivered?

Many tia
2 Solutions
You are seeing the old BCC trick. Very common spammers trick. Means that they can send one email address with 100s of email address in the BCC field and the recipients don't see any of the addresses.

Your AV/AS software should be able to filter email messages from your own domain. However if you have any users who send email from your domain using Outlook Express and have to send through their own SMTP server, they will not be able to send email in to your site with their from address as your domain.

if you have no pop3 clients you can just tell your gateway to block inbound emails with a from address with your domain. thats what i did. Like the above poster said this will not work if you use pop3 clients.

Also i beleve exchange 2003 sp2 has a feature for this, but i would rather block it at the gateway

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