Inbound Proxy Internal Send Connector - 451 4.7.0 Timeout waiting for client input RRS feed

  • Question

  • Hi there,

    Short version :

    Exchange internal proxy transport keeps connection open, and gives a timeout after 5 minutes receiving code 451 4.7.0

    The whole story :

    After some mail troubles with an internal application I started to dig into the Exchange 2016 log files.
    We migrated a short time ago from 2010 to 2016, and have 2 Exch2016 servers running with a DAG.
    At this moment we are running version 15.1 build 845.34

    I see a lot of timeout errors in the HUB SMTP receive logs.  Mostly this is between the two Exchange servers, sometimes even within the same server; internal communication)
    If I check the SMTP Send protocol logfiles from the other side, I can see in 1 such particular session that a lot of e-mails are proxied to the other server, separated by a RSET command.
    At the end of the session there is no activity for 5 minutes, and then a QUIT is send to the receiving Exchange server immediately followed by an incoming "451 4.7.0 Timeout waiting for client input" from the receiving server.  (Ordered on Sequence Number)

    On the receiving server I see the sending of the timeout, but cannot see any incoming QUIT command from the sending server. I suspect this QUIT is sent after receiving the timeout, although sequence number tells something else.

    I tried raising the inactivity timeout for the receive connector, thinking they are both timing out after 5 minutes and thus sending timeout and quit at the same time, but this didn't work.
    Now bot QUIT and timeout are sent after 6 minutes of inactivity.

    As far is I know, no mail is lost and everything is working correctly.

    So my questions are:

    1. Is this normal behavior ?
    2. Can I do something to prevent these timeouts to happen ?
    3. Does this incidate other problems and should I check/fix something else ?

    Thanks in advance !

    Friday, June 22, 2018 12:08 PM

All replies

  • Hi Steven Broos,

    Since your mail flow is normal, I think this phenomenon isn't a issue.


    Kyle Xu

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    Monday, June 25, 2018 8:37 AM
  • Hi Kyle,

    I think it isn't an issue, but I don't feel comfortable by this situation.
    If this is "normal" maybe I should file a bug report that the connection is not closed properly ?
    Or maybe there IS a problem, not causing any troubles (yet), but I should investigate further ?

    Wednesday, June 27, 2018 10:53 AM