none
500 5.3.3 unrecognized command issue

    Question

  • Hi all, 

    My client has an issue where random senders within, and outside of the organization will receive a "Remote Server returned '500 5.3.3 Unrecognized command' error when sending mail to a certain address. This only happens with one particular user. We checked the firewall and made sure smtp filtering wasnt enabled, made sure AV wasnt filtering as well. Sent test emails from external email and internal, can't replicate this issue. It happens randomly. 

    I am running Exchange Server 2010 Standard service pack 1. Does anyone have any suggestions or input on what may be going on?

    Thursday, May 26, 2016 5:10 PM

Answers

  • Ask the postmaster of the mail service that one particular user is using.

    You can enable SMTP logging on the send connector and review the SMTP logs for more detail about the bounce.


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

    Thursday, May 26, 2016 6:07 PM
    Moderator
  • Hi all, 

    My client has an issue where random senders within, and outside of the organization will receive a "Remote Server returned '500 5.3.3 Unrecognized command' error when sending mail to a certain address. This only happens with one particular user. We checked the firewall and made sure smtp filtering wasnt enabled, made sure AV wasnt filtering as well. Sent test emails from external email and internal, can't replicate this issue. It happens randomly. 

    I am running Exchange Server 2010 Standard service pack 1. Does anyone have any suggestions or input on what may be going on?

    You should ask the mail admin on the other side if they can enable some logging on their receive connectors and see if they spot anything.  Also, SP1 is pretty old Exchange 2010.  You should consider updating to SP3 and the latest RU.

    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread

    Thursday, May 26, 2016 6:09 PM

All replies

  • Ask the postmaster of the mail service that one particular user is using.

    You can enable SMTP logging on the send connector and review the SMTP logs for more detail about the bounce.


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

    Thursday, May 26, 2016 6:07 PM
    Moderator
  • Hi all, 

    My client has an issue where random senders within, and outside of the organization will receive a "Remote Server returned '500 5.3.3 Unrecognized command' error when sending mail to a certain address. This only happens with one particular user. We checked the firewall and made sure smtp filtering wasnt enabled, made sure AV wasnt filtering as well. Sent test emails from external email and internal, can't replicate this issue. It happens randomly. 

    I am running Exchange Server 2010 Standard service pack 1. Does anyone have any suggestions or input on what may be going on?

    You should ask the mail admin on the other side if they can enable some logging on their receive connectors and see if they spot anything.  Also, SP1 is pretty old Exchange 2010.  You should consider updating to SP3 and the latest RU.

    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread

    Thursday, May 26, 2016 6:09 PM