Can Windows Server 2008 R2 SMTP running on IIS 6.0 supports IPv6?


  • Understand that even if we were to install SMTP feature in Windows Server 2008 R2, the SMTP features will still runs on IIS 6.0.
    My Infra is moving to IPv6. Then, I saw this article from Microsoft TechNet - "How IIS 6.0 Supports IPv6 (IIS 6.0)"

    In the article, it actually states under "Differences in IIS Functionality Between IPv4 and IPv6:
    File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), and Network News Transfer Protocol (NNTP) services are not supported. IPv6 is supported only for the WWW service. The FTP, SMTP, and NNTP services do not have IPv6 support in IIS 6.0.

    So, my question is if we need SMTP Relay in my infra to run on Windows Server 2008 R2;and must run IPv6, How?! Or the article is referring that it will still work but there will be no support? Anyone can advise?
    Many Thanks
    Tan Chee

    Tuesday, January 22, 2013 6:54 AM

All replies

  • First, I doubt your infrastructure will be completely IPv6 with no IPv4 capabilities (of course what I doubt really doesn't matter).

    Next, IIS 6.0 is for Windows Server 2003 and has next to nothing to do with Windows Server 2008 R2 which uses IIS 7.5. Also, IPv6 support in Windows Server 2003 was never more than an experimental after-thought but is completely integrated into Windows Server 2008 R2.

    Thus that article is is completely not applicable to Windows Server 2008 R2 and IIS 7.5. You should ignore it. I have no definitive reference to state that SMTP services in Server 2008 R2 are supported on IPv6 but have no doubt that they are because as stated, IPv6 is a fully integrated and supported protocol stack in Server 2008 R2.

    Jason |

    Tuesday, January 22, 2013 2:41 PM
  • Hi Jason,

    Thanks for responding. So, what you mean is that SMTP feature on Windows Server 2008 R2 has nothing to do with IIS6.0 that was installed together when you add the SMTP feature? The IIS6.0 is only the console to manage the SMTP feature?

    So, when I turn on dual stack on the Windows Server 2008 R2 box with SMTP, there should be no impact?

    Sorry. Got very confused after reading too much what is available on the internet.


    Tan Chee

    Monday, January 28, 2013 7:56 AM
  • As mentioned, Server 2008 R2 does not use IIS6. The MMC snapin is just an admin console and not indicative of the IIS version, SMTP capabilities, or IPv6 capabilities of the OS.

    In general, yes to your question; however, there's a lot more to using and making IPv6 work that just enabling it as a protocol on the server.

    Jason |

    Monday, January 28, 2013 2:06 PM
  • Not quite the way I experience SMTP service on Windows 2012 for example.

    When you add SMTP feature, the legacy IIS6 is installed. SMTP service can be managed via IIS6 console, as you mentioned. But the console GUI has no support for IPv6. One can not configure it to listen on IPv6 interface, setup IPv6 allowed-to-relay address spaces etc.

    Unless there is some command line or direct IIS6 metadatabase editing way to support IPv6 configuration, I am afraid the SMTP service is just as good-<g class="gr_ gr_520 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" data-gr-id="520" id="520">ol</g>' IIS6 as the console itself.

    The `<g class="gr_ gr_382 gr-alert gr_spell gr_inline_cards gr_run_anim ContextualSpelling ins-del multiReplace" data-gr-id="382" id="382">netstat</g>` confirms the SMTP service is listening on IPv4 only.

    Friday, May 5, 2017 10:14 AM
  • Although this is a few years after the fact, there is a simple way to let the SMTP server listen on IPv6:

    netsh int portproxy add v6tov4 listenport=25 connectport=25

    This is a simple port forwarder, but it will let IPv6 clients connect to your mail server. Outgoing connections can go the other way via similar means. 

    • Proposed as answer by Rozi Saturday, February 3, 2018 7:23 AM
    Friday, January 19, 2018 8:55 AM
  • Jeroen, thank you for your reply. It seems a perfect solution, however, it has an issue one needs to be alert of.

    IPv6 requests are proxied to the IIS SMTP service from This makes SMTP service believe the proxied request is originating from the localhost, effectively letting it relay mail.

    To prevent your IIS SMTP service to become an open IPv6 mail relay, use the firewall to allow IPv6 access to your TCP 25 port from the trusted IPv6 segments only.

    Wednesday, March 7, 2018 9:13 AM