Problem sending mail "Client host rejected: Sorry, no xDSL here"

I'm trying to use SMTP on localhost to send emails thru a simple mailform in asp.net c#. For some reason all emails end up on the badmail folder. The .BAD file says:

Fina开发者_如何学运维l-Recipient: rfc822;xxxx@xxxx.com.br
Action: failed
Status: 5.7.1
Diagnostic-Code: smtp;554 5.7.1 <IP>: Client host rejected: Sorry, no xDSL here

Anybody got any clue?

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https://serverfault.com/questions/100007/problem-sending-mail-client-host-rejected-sorry-no-xdsl-here

put it on serverfault.com