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.NET Framework Developer Center > .NET Framework Forums > Network Class Library (System.Net) > SmtpClient.Send hangs - no network traffic to SMTP server

Unanswered SmtpClient.Send hangs - no network traffic to SMTP server

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      Thursday, February 25, 2010 4:13 AM
       
       
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      Web searches for this issue kept turning up folks having firewall problems which is not the case here (can send Database Mail from SQL server without issues).

      I am writing a Windows console app in V Studio 2008 Pro which contains the following code, which I've stripped down to two lines trying to troubleshoot.

       

      SmtpClient mailServer = new SmtpClient("smtp.mydomain.com");
      mailServer.Send("nobody@mydomain.com", "myaddress@msn.com","test", "test");

      I execute the above code while I have Wireshark running and observe the following
        - My system sends a SYN packet to the SMTP server
        - The SMTP server replies with a SYN ACK
        - My system sends an ACK
        - The SMTP server replies with a response code 220
        - Another ACK is sent from my system to the SMTP server
        - Program hangs until the call times out and throws a SmtpException.

      So everything looks like what I'd expect until the SMTP server sends the response code - it is almost like SmtpClient is ignoring it and I'm really not sure why the second ACK is sent.

      The SMTP server does not authenticate, I checked in the debugger and the "Credentials" property is null and "UseDefaultCredentials" is false.

      Am I missing something obvious?

       

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    • Monday, March 01, 2010 9:06 PM
       
       
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      Have you tried System.Net tracing? http://msdn.microsoft.com/en-us/library/ty48b824.aspx

      It may shed a bit more light on what's going wrong.

      Also, does the async code path behave any different?

       
    • Sunday, March 21, 2010 11:58 PM
       
       
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      Thank for for your reply, sorry it took me a while to re-reply.

       

      Actually out of desperation I tried re-targeting my executable for the .Net 2.0 runtime and that seemed to fix my problem. No idea why, but whatever the reason the fix is good enough for me.

       
    • Saturday, November 20, 2010 4:20 AM
       
       
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      Yikes, sorry it took me so long to follow up again everyone. I'm pretty sure my problem went away on it's own - out of desperation I retargeted my application to the .Net 2.0 framework and everything started working.

      I have no faith whatsoever that using an older framework actually changed anything, I think something on the mail server must have been fixed at the same time I was tinkering with my code.