messages can't be sent


  • Hi, 

    I had Exchange 2013 sever deployed, however, I can't send messages out with the error message "Unrecognized command". Can you help?

    Unrecognized command
    Thursday, November 23, 2017 9:16 AM


All replies

  • Hi

    Kindly check remote server has enough storage capacity to hold mail and check the SMTP log.

    Please mark as an "Answer" and do "Vote",if my contribution or answer is useful

    Thursday, November 23, 2017 9:47 AM
  • Hi,

    Does this issue occur when sending to any external domains? Have you open the 25 port on your firewall? To my experience, the 5.3.3 Unrecognized command issue often occurs when the Exchange server is behind a firewall and the Auth and Auth login Extended Simple Mail Transfer Protocol (ESMTP) commands are removed by the firewall which is explained in the following article:



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    Thursday, November 23, 2017 9:52 AM
  • thanks, it turned out that the security software blocked the port. After enabled it, I can send email now.
    Friday, November 24, 2017 6:22 AM