I have a SMTP relay server running on a hosted server under IIS, that uses a direct send configuration. I have migrated our old hosted exchange, to cloud exchange on office365 side and had to created a SMTP relay for our printers, scripts, etc with less security features be able to send notifications to our emails in cloud exchange.

Two months later, we had already our SMTP relay public IP being blocked by spamhaus with CSS and XBL triggers, more than 10 times, and we are still counting. We have that static public IP added in DNS Record on SPF like Microsoft Said, but still nothing.

There is no intranet devices hijacked and sending massively through that relay, I have already check and recheck logs generated by that relay.

Anyone knows what can be or how to solve?

1 Answer 1


Which method do you use to configure smtp relay mentioned in the article?

You could check steps mentioned in the article.In addition, i have found a similar thread and there were some discussions on this issue for your reference:My Internet Static IP is black listed as spammer.. how to solve this !

  • I have configured option 3. I have read several similar to that one, but this is not an open relay to internet, its only accessable from certain internal devices. There is no external port forwarding for that SMTP relay at 25 port.
    – marafado88
    Nov 16, 2020 at 12:27

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