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Reject SMTP Traffic at Virtual Server

Jens Dellner

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we want to load balance smtp Traffic. Since now the IPs which are allowed to send smtp were restricted at the Mail Server.


We use Listen Policies on our Virtual Server to restrict the IPs which are allowed to send smtp to the Virtual Server. And we only allow the Exchange servers to process smtp sent from the VIP. This works, but it is bad for troubleshooting purposes. The Client does not get a Status Code back from the Virtual Server that his SMTP sending was rejected; because it was dropped.


I found a Blog entry about a Palo Alto Feature which can reject smtp Traffic with a status code of 541 "Recipient Address Rejected – Blacklist, Anti-Spam, Mailfilter/Firewall Block” ( https://blog.webernetz.net/palo-alto-blocks-smtp-virus-with-541-response/ ).


Is there any way to block the smtp Traffic on the Virtual Server and send back a status code? It is possible to respond with a html Page, SQL OK, SQL Error and DNS but I didn´t find any hint that it is possible for smtp in any way?


I appreciate your help!


Best regards,

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