SpamFilter has a filter that stops emails when the “from” and “to” email domains are the same - you can find its location by following the screenshot at:

www.logsat.com/sfi-spam-filter-screenshots/sfi-filtering-options.asp

Please note that this filter is very restrictive - it's either on or off, thus it is very restrictive. There is a new standard called “SPF” (Sender Policy Framework) that is used to prevent similar problems that was created a few years ago. In simple terms, it allows you to define via DNS what IP networks are allowed to send emails from your domain.
This addresses for example the issue of credit card merchants sending email confirmations to customer who have purchased products, where the company selling the product is one of your own customers (or yourselves). The emails will usually be "From" an email address in your domain, but as the credit card's company is "faking" the sender's address and sending the email from their own servers, it would be rejected if you were to receive it with that from/to filter on. With SPF, you can specify in a DNS TXT record that the IP address of the merchant is allowed to send email on your behalf, and thus not cause any problems.
This will practically eliminate all spam sent to your domain using your own domain name as a sender.