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Re: Problem with line which is longer than 256 characters

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  • Wietse Venema
    ... A tcpdump recording will reveal if the client stops sending or if the server stops reading (it s revealed by TCP receive window size). Once this is known
    Message 1 of 4 , Feb 11 2:36 PM
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      Rolf E. Sonneveld:
      > In general, Postfix is running fine and this Postfix instance is also
      > running fine. However, there is one SMTP client (of which we are not in
      > control), that sends messages with long lines to this server running
      > Postfix. There is a problem with the communication between this client
      > and the server: whenever the clients sends a message which includes one
      > long line (377 characters, excluding the CRLF), the client seems to
      > 'hang' after character # 256 of this long line is transmitted. Then,
      > after some time the connection times out.

      A tcpdump recording will reveal if the client stops sending or if
      the server stops reading (it's revealed by TCP receive window size).
      Once this is known the search can be focused. It could be somethinh
      as stupid as poorly-implemented anti-virus software.

      http://www.postfix.org/DEBUG_README.html#sniffer

      Wietse
    • Rolf E. Sonneveld
      ... thanks for your answer. I did a tcpdump for the session but when analysing it, I could not find a clear cause. At the end of the day, it appeared to have
      Message 2 of 4 , Feb 16 8:16 AM
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        On 02/11/2013 11:36 PM, Wietse Venema wrote:
        > Rolf E. Sonneveld:
        >> In general, Postfix is running fine and this Postfix instance is also
        >> running fine. However, there is one SMTP client (of which we are not in
        >> control), that sends messages with long lines to this server running
        >> Postfix. There is a problem with the communication between this client
        >> and the server: whenever the clients sends a message which includes one
        >> long line (377 characters, excluding the CRLF), the client seems to
        >> 'hang' after character # 256 of this long line is transmitted. Then,
        >> after some time the connection times out.
        > A tcpdump recording will reveal if the client stops sending or if
        > the server stops reading (it's revealed by TCP receive window size).
        > Once this is known the search can be focused. It could be somethinh
        > as stupid as poorly-implemented anti-virus software.
        >
        > http://www.postfix.org/DEBUG_README.html#sniffer

        thanks for your answer. I did a tcpdump for the session but when
        analysing it, I could not find a clear cause. At the end of the day, it
        appeared to have been a cli/tty related limitation (of Solaris?). See
        for a discussion
        https://forums.oracle.com/forums/thread.jspa?messageID=8292168). When
        sending the same data using a perl script it worked without a problem.

        /rolf
      • Wietse Venema
        ... Based on the bits on the wire it is 100% clear whether the client stops sending or whether the receiver stops receiving. Just look at the TCP window.
        Message 3 of 4 , Feb 16 3:29 PM
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          Rolf E. Sonneveld:
          > On 02/11/2013 11:36 PM, Wietse Venema wrote:
          > > Rolf E. Sonneveld:
          > >> In general, Postfix is running fine and this Postfix instance is also
          > >> running fine. However, there is one SMTP client (of which we are not in
          > >> control), that sends messages with long lines to this server running
          > >> Postfix. There is a problem with the communication between this client
          > >> and the server: whenever the clients sends a message which includes one
          > >> long line (377 characters, excluding the CRLF), the client seems to
          > >> 'hang' after character # 256 of this long line is transmitted. Then,
          > >> after some time the connection times out.
          > > A tcpdump recording will reveal if the client stops sending or if
          > > the server stops reading (it's revealed by TCP receive window size).
          > > Once this is known the search can be focused. It could be somethinh
          > > as stupid as poorly-implemented anti-virus software.
          > >
          > > http://www.postfix.org/DEBUG_README.html#sniffer
          >
          > thanks for your answer. I did a tcpdump for the session but when
          > analysing it, I could not find a clear cause.

          Based on the bits on the wire it is 100% clear whether the client
          stops sending or whether the receiver stops receiving. Just look
          at the TCP window.

          Wietse

          > At the end of the day, it
          > appeared to have been a cli/tty related limitation (of Solaris?). See
          > for a discussion
          > https://forums.oracle.com/forums/thread.jspa?messageID=8292168). When
          > sending the same data using a perl script it worked without a problem.
          >
          > /rolf
          >
          >
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