Mailbox unavailable. The server response was: 5.7.1 Unable to relay for abc@xyz.com [closed]

Answer 1

Aahh got it... I got it working :)

Thanks Christopher, your suggesion is correct.

But, finding "Default SMTP Virtual Server" was tricky ;)

Even if you use IIS7 to deploy your web site, you have to open IIS6 Manager to configure SMTP server (why?).

I configured SMTP server as follows to make things work:

1. Open IIS6 Manager using Control Panel --> Administrative Tools.
2. Open SMTP Virtual Server properties.
3. On General tab, Set IP address of the Web server instead of "All Unassigned".
4. In Access tab, click on Relay button, this will open Relay Restrictions dialog.
5. In relay computers list, add the loopback IP address i.e 127.0.0.1 and IP address of the Web server, so that they can pass/relay emails through the SMTP server.

Answer 2

Wanted to share what caused the error in my case. Spend couple hours to figure this out, so hopefully it will help to save someone some time.

Strangely enough, the error was raised with the Enable drop directory quota setting being enabled for the domain.

I am not the expert and don't know the technical explanation, but unticking the mentioned setting sorted the problem.