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Editorial Team
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Asked: 2026-05-15T16:23:03+00:00

I am getting Mailbox unavailable. The server response was: 5.7.1 Unable to relay for

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I am getting “Mailbox unavailable. The server response was: 5.7.1 Unable to relay for abc@xyz.com” when I try to send the mail using ASP.NET. The site is deployed on IIS7, Windows 2008 server.

The website was working fine on IIS6 and Windows 2003 Server. I deployed it on IIS7, 2008 it has started giving me this error.

Has anybody experienced this before?

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1 Answer

  1. Editorial Team

    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.
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