none
OutBound mail flow fails to send and stuck in query 451.4.4.0

    Question

  • Hello,

    The test exchange server I'm trying to deploy passes all connectivity tests but is having trouble sending anything outbound. it can receive from the outside just fine. We've  already processed our reverse delegation DNS request through our ISP and it's up and running.

    Mail just gets stuck in queue and keeps trying to retry with the 451.4.4.0 error encountered while communicating with primary target IP addresses then ends up failing to send with the header #550 4.4.7 QUEUE.Expired; message expired ##

    Monday, January 11, 2016 11:03 PM

Answers

  • Have you tried testing sending a message from the server using telnet to port 25 to an Internet server?

    Also you could enable verbose protocol logging on the relevant send connector(s) and looking at the SMTP transactions.


    Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
    Celebrating 20 years of providing Exchange peer support!

    Monday, January 11, 2016 11:58 PM
    Moderator

All replies

  • Have you tried testing sending a message from the server using telnet to port 25 to an Internet server?

    Also you could enable verbose protocol logging on the relevant send connector(s) and looking at the SMTP transactions.


    Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
    Celebrating 20 years of providing Exchange peer support!

    Monday, January 11, 2016 11:58 PM
    Moderator
  • Hi,

    Have you enabled the option " force the send connector to use the external DNS settings for the transport server" on the send connector side. I saw some same issue was solved when enabling the option.

    Then try to restarte the MSExchangeTransport service .

    Also check some related application event logs on the Exchange server.

    Regards,

    David 

    Tuesday, January 12, 2016 3:08 AM
    Moderator
  • Better than that is to make sure that the DNS servers the Exchange server is using can resolve Internet names.

    Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
    Celebrating 20 years of providing Exchange peer support!

    Tuesday, January 12, 2016 5:10 AM
    Moderator
  • Few questions to understand the issue

    1- How your send connector configured to send out emails ? Using DNS or Smarthost

    2- Is it happening for any specific recipient domain ?

    As suggested by ED, i would prefer to enable the logging and then see what wrong is there also you can check as David suggested.

    If your server getting the primary target IP then seems DNS working fine to get the target IP where it needs to deliver.

    Did you enable any specific authentication in send connector?


    Mihir Nayak If a post is helpful, please take a second to hit the green arrow on the left, or mark as answer, thanks

    Tuesday, January 12, 2016 5:34 AM
  • ended up finding out that AT&T was blocking port 25 to go out. should've done more researched. this was helpful finding out the problem though. Thanks
    Tuesday, January 12, 2016 6:59 PM
  • That is normal for a residential-class Internet service to reduce the case where people's PCs are turned into spam-generating monsters.

    You're welcome, happy to have helped.  Glad you got it sorted out.

    You can probably route your SMTP through their SMTP server, but that will likely kick in recipients' antispam filters.


    Ed Crowley MVP "There are seldom good technological solutions to behavioral problems."
    Celebrating 20 years of providing Exchange peer support!



    Tuesday, January 12, 2016 11:35 PM
    Moderator