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5.7.3 STARTTLS is required to send mail RRS feed

  • Question

  •  Hej,

     I have a hybrid Exchange 2016 env. Now I get a lot of these errors I get his error on Connector name "Outbound to 0402d62e-ee9a-452e-909b-7223877xxxxx"

     Reason: [{LED=450 4.4.317 Cannot connect to remote server [Message=451 5.7.3 STARTTLS is required to send mail] [LastAttemptedServerName=mail.xxxxx.xx] [LastAttemptedIP=193.x.xxx.141:25] [DB3EUR04FT063.eop-eur04.prod.protection.outlook.com]};{MSG=451 5.7.3 STARTTLS is required to send mail};{FQDN=mail.xxxx.xx};{IP=193.x.xxx.141  OutboundProxyTargetIP: 193.x.xxx.141. OutboundProxyTargetHostName: mail.xxx.xx

     Certifikat er ok, As far as I know no changes have been made, Do you have any ideas what can cause this? 

    thanks


    Erro


    • Edited by Erró Monday, January 28, 2019 10:11 AM
    Monday, January 28, 2019 10:09 AM

Answers

  • Hi,

    You could take these into consideration:

    1. Please check and turn off the firewall or any other scanning software temporarily.

    2. Make sure the sending server's IP is not on an SMTP block list.

    3. Verify that the receiving server is configured to use TLS.

    4. Check if the receiving server is configured to only respond to SMTP (not ESMTP) commands. TLS is part of the ESMTP protocol.

    Additionally, here is a similar issue, and you may get some useful information from it: Mail flow stop from Office 365 to On-premise exchange server

    Regards,

    Lydia Zhou


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Tuesday, January 29, 2019 9:34 AM

All replies

  • https://docs.microsoft.com/en-us/office365/securitycompliance/mail-flow-intelligence-in-office-365

    https://support.microsoft.com/en-ph/help/2989382/can-t-receive-mail-in-a-hybrid-environment-after-you-install-a-new-cer


    “Vote As Helpful” and/or “Mark As Answered” - MCSA - MCSE - http://www.ucsteps.com/

    Monday, January 28, 2019 11:13 AM
  •  Hi Thiago,

      I have already  seen both this, and they do not help me. The certifikat is valid.

     


    Erro

    Monday, January 28, 2019 12:17 PM
  • Hi,

    You could take these into consideration:

    1. Please check and turn off the firewall or any other scanning software temporarily.

    2. Make sure the sending server's IP is not on an SMTP block list.

    3. Verify that the receiving server is configured to use TLS.

    4. Check if the receiving server is configured to only respond to SMTP (not ESMTP) commands. TLS is part of the ESMTP protocol.

    Additionally, here is a similar issue, and you may get some useful information from it: Mail flow stop from Office 365 to On-premise exchange server

    Regards,

    Lydia Zhou


    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Tuesday, January 29, 2019 9:34 AM