I am trying to configure IIS 6 SMTP server for outbound mail. I did the following telnet test from Wikipedia and getting error highlighted in bold below.

220 smtp.example.com Microsoft ESMTP MAIL Service, Version: 6.0.. ready at
Me: HELO smtp.example.com
Telnet: 250 Hello smtp.example.com []
Me: MAIL FROM: bob@example.org
Telnet: 250 2.1.0 bo@example.org....Sender Ok
Me: RCPT TO: alice@gmail.com
Telnet: 550 5.7.1 Unable to relay for alice@gmail.com

I am using the default SMTP Virtual Server configuration. Do i need to make any configuration changes to resolve this error?

Thanks for reading!

UPDATE: THe issue got fixed by using the IP address of the machine, not the localhost or Thanks everyone for your replies.


If you're going to be sending email directly from the IIS SMTP server, then you don't need to configure any relay settings. The server sending outbound email from itself is not a relay. The tests you're running are exactly what you should expect when trying to send email through the server from another host (because relaying is not enabled). IIS SMTP is a fully functional SMTP server, and as such, requires no relay configuration unless other hosts will be sending email through it to external domains (domains not native to the IIS SMTP server). Again, if the IIS SMTP server will be sending email from itself to external domains, no relay configuration is required.

  • Email submitted through the "Pickup" directory wouldn't be considered relaying. I suppose that's what you mean by "a fully functionla SMTP server". The poster doesn't seem to be referring to using the "Pickup" directory, though. Any email received via SMTP over TCP connection, even from the server itself, is considered relaying by IIS. – Evan Anderson Oct 13 '09 at 19:49

This isn't an error. Your server is telling you that it's been configured not to "relay" (that is, send on to another server) mail. That's generally good. You don't want to attach an SMTP server to the Internet that can relay mail to anywhere, because spammers will find it in a very short time and start using it to deliver email on their behalf.

Have a look at the "Relay..." settings on the "Access" tab of the properties for the SMTP server. You can specify IP addresses of clients that are allowed to relay, and can allow authenticated users to relay (which is ticked by default).

If you absolutely can't configure your clients to authenticate, allowing them to relay by IP address or range of IP addresses is acceptable. Allowing the world to relay on a machine that's connected to the Internet isn't, and, to my mind, it's not acceptable to do so on a LAN either (though others' opinions will, no doubt, differ from mine).

  • @Evan: I am blocking external IPs from using the SMTP server for relay. But, would like to use it only from the localhost machine. I have added the IP address of machines to the "Relay" option in "Access" tab. But, it would still say the same error message. I ran the tool SmtpDiag. It threw one error "Failed to connect to the domain controler. Error: 8007054b", but ran all tests sucessfully. What do you think should i look next? Thanks! – pencilslate Oct 13 '09 at 17:47
  • Did you add to the list of machines allowed to relay? – Evan Anderson Oct 13 '09 at 18:42

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