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Mailsot name resolution in windows 10 1803 RRS feed

  • Question

  • Hi,

    Does anyone know what  changed in Windows 10 1803  that would make my programs running on the same PC are   not able to address a mailslot to 

    \\machinename\mailslot\win901  (win901 is the name I have decided for this mailslot)

    but the resolution \\.\mailslot\win901 is working.

    I have set LMHOST, even WINS server, with the PC IP Address, no firewall active 

    Any idea what I should look for?




    Wednesday, May 16, 2018 8:21 PM

All replies

  • Hello,

    We (as an ISV) have the exact same problem here, no workaround at the moment

    Hopefully Microsoft will acknowledge the problem, we are waiting for a solution...


    Thursday, May 17, 2018 1:21 PM
  • Found this same issue in software that has worked for 15+ years.  It seems like a new bug in 1803.  CreateFile on a mailslot fails with Error 53 ERROR_BAD_NETPATH when creating a mailslot using anything other than \\.\ even a reference to the same local machine.

    I think it's a bug since on the same computer, mailslots may be created and receive messages. If it were a feature removal or tightening of security, they presumably would have also disabled mailslot creation and ability to receive messages.

    I had posted more details previously to technet and stackoverflow.

    Friday, May 18, 2018 4:50 PM
  • Same exact issue here.

    Software flawlessy working for 15+ years now abruptly stop with ERROR_BAD_NETPATH (53) error.

    It is relates to MailSlots IPC mechanism somewhat messed up by latest 1803 Win10 update.

    This issue has so many regressions on legacy software i expect Microsoft to react with an emergency hotfix, or they will be in real troubles.

    Tuesday, May 29, 2018 8:18 AM
  • Note that because this is a bug (possibly just in the way CreateFile validates UNC path names), there are a few things you can leverage to workaround it:

    1) you can still receive messages fine, whether sent from the same computer using \\.\mailslot\slotName or another computer (that is not running 1803)

    2) you can still send to a local mailslot by using \\.\mailslot\slotName, but not \\localComputerName\mailslot\slotName

    3) you can still broadcast to slots on any other computer using \\*\mailslot\slotName.  Odd that this still works but helpful because easy broadcast messages are one of the benefits of using mailslots.

    It would be hacky, but you could broadcast all your mailslot messages for now or use a hacky naming scheme like: \\*\mailslot\slotName\computerName instead of sending to just \\computerName\mailslot\slotName.  OR If you have a centralized send function, it's not too hard to route direct messages to other computers via a socket, named pipe, or other means rather than using the now-broken mailslots.

    Wednesday, May 30, 2018 8:41 PM