Getting 550 you have been detected sending spam on offsite Exchange clients using Outlook and POP3


  • Very recently, offsite SBS2008/Exchange 2010/ Windows7/ Outlook clients have been getting an error "550 Your message has been rejected because you have been detected sending spam" when attempting to send emails from outlook. This message comes from "System Administrator" and when I look at the message properties, there are no Internet headers. This occurs in what appears to be a somewhat random fashion.  When offsite, they are set to default to a POP3 account for sending offsite and initially I thought the problem was that the account was somehow switching to the "exchange account" to send (and maybe it is). But normally if this occurs, the message just gets stuck in the Outbox.  Any assistance is greatly appreciated.

    Patrick H

    • Edited by ITPatrick Friday, April 14, 2017 5:21 PM title fix
    Friday, April 14, 2017 5:15 PM

All replies

  • Hi Patrick,

    Please check the following points to narrow down the issue to Outlook clients or Exchange side settings:

    1. Does the issue only happen to one specific user?
    2. Could you provide the complete NDR message content which comes from System Administrator for more information?
    3. Confirm if the issue only occurred when using POP3 connection for this Exchange account.
    4. Try to use OWA (Outlook Web App) to sent the same message to same sender, confirm if the issue can be reproduced or email can be sent successfully.
    5. For POP3 connection, please go to Account Settings, double-click this account, click More Settings, under Outgoing Server, make sure the following setting in checked:
    6. Why not directly using Exchange connection for message sending instead of POP3 connection?


    Winnie Liang

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    Monday, April 17, 2017 8:11 AM
  • Hi Winnie Liang,

    Thank you for taking the time to respond. I am not sure I can get an NDR report. The email is going out of Outlook using a POP3 account when the user is offsite, and the email rejection contains no internet header information. I did use wireshark to capture the data and it shows that at least the emailing computer is talking to the far end emailserver before getting rejected. I did not see in my captured logs the reason, but I am new to wireshark so I plan to see if it may be in the capture somewhere.  I had another user who had emails not getting delivered to a particular person, we used a third party tracking tool to send a message and got the following data at the end of the communication ( the mail was not received, and we got no notification of such). So I am wondering now if this is the cause of the bounce backs from our SMTP provider as well. I actually started a separate thread, because at the time I thought these to be too separate issues.

     354 enter mail, end with “.“ on a line by itself\n 2017-04-17 15:33:12 <<< .\n 2017-04-17 15:33:12 >>> 552 5.2.0 Invalid 7bit DATA\n 2017-04-17 15:33:12 <<< QUIT\n 2017-04-17 15:33:12 >>> xxx x.0.0 name.of.a.remote.server bizsmtp closing connection\n 2017-04-17 15:33:12 closed ( in=551 out=6449\n 2017-04-17 15:33:12 done

    Patrick H

    Thursday, April 20, 2017 7:37 PM