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How to lock port 25 in Exchange Server 2016 RRS feed

  • Question

  • I'm trying to lockdown the port 25 in our Exchange server by removing the "Anonymous Users" in Security option in our Receive Connectors (Default Frontend <ServerName>) but when I tried to send an email to our Exchange Server 2016 using external emails (Yahoo, GMail), we are getting a bounce-back says "status=bounced (host mail.domain.com[X.X.X.X] said: 530 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM (in reply to MAIL FROM command))". 

    How can I properly lock down port 25?

    Thank you,

    Sunday, June 21, 2020 11:14 PM

All replies

  • Hi,

    What do you mean "lockdown the port 25"? Please provide more details about your requirements.

    The default receive connector "Default Frontend <ServerName>" is used to accepts anonymous connections from external SMTP servers. If you remove permissions for "Anonymous Users", external messages cannot be accepted and can lead to your issue "530 5.7.57 SMTP; Client was not authenticated to send anonymous mail during MAIL FROM". For more information about receive connectors, you can check: Default Receive connectors created during setup.

    Additionally, it's not suggested to modify the default receive connectors. If you want to accept specific messages with a receive connector, you can custom a new receive connector. 

    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.

    Monday, June 22, 2020 3:22 AM
  • Hi,

    Just checking in to see if above information was helpful. If you have any questions or need further help on this issue, please feel free to post back. 

    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.

    Thursday, June 25, 2020 8:57 AM