SMTP Errors - Black Hole Router

Discussion in 'Windows Small Business Server' started by CDP, Feb 8, 2007.

  1. CDP

    CDP Guest

    It's been awhile, but several months ago, we setup a SBS 2003 with Exchange.
    We had all kinds of problems with getting mail to go out using SMTP. We
    tried all kinds of setting changes on the server, with our ISP, etc., etc.
    The people here on this forum suggested all kinds of things that we could be
    doing wrong with Exchange and our mail setup, but nothing worked.

    So, we had to "bite the bullet" and make a paid call to Microsoft support.
    After several days and hours of phone support, we found that the 2Wire
    2700HG-B DSL modem/router supplied by AT&T/SBC has this problem:

    http://support.microsoft.com/kb/314825/en-us

    Basically, the router does not respond correctly when it gets too large of a
    packet to send. Instead of responding back that the packet needs to be
    broken up into smaller fragments, the transmission times out and the packet
    gets dropped.

    For a work-around, we did method 1 in the above article to our SBS, but that
    didn't work. AT&T was not able to provide any further help, so we couldn't
    do method 2. Method 3 ultimately fixed the issue.

    Looking back upon things, other symptoms that had occurred before the
    implementation of the Exchange server is that we at first were only using
    the SBS as a DHCP server and gateway. When clients on the network tried to
    send mail through Outlook and the ISP's SMTP server, we had similar problems
    where mail was not going out due to the router dropping large packets and
    not responding back with the appropriate response.

    Hope this might help other people, especially with this 2Wire modem/router
    being so popular.

    Thanks to everyone for their help!
     
    CDP, Feb 8, 2007
    #1
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  2. And thanks for posting back and showing the value of this community
     
    Cris Hanna [SBS-MVP], Feb 8, 2007
    #2
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