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Direct Send allows SMTP relay to external recipients?

Anonymous
2017-05-02T19:52:48+00:00

Microsoft's article here: https://support.office.com/en-us/article/How-to-set-up-a-multifunction-device-or-application-to-send-email-using-Office-365-69f58e99-c550-4274-ad18-c805d654b4c4

....says that "Direct send cannot be used to deliver email to external recipients, for example, recipients with Yahoo or Gmail addresses.", but I have found that doesn't seem to be true. I can use any MX record for anyone that uses Office 365, connect to it via SMTP, and send to external recipients (like Gmail, another O365 tenant, etc.).

I thought that only the "SMTP relay" method was supposed to allow this, so you can create the connector and add an allowed static IP address.

Why does "Direct send" also allow delivery to external recipients with no authentication? Seems like a security risk!

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  1. Anonymous
    2017-05-08T09:40:05+00:00

    Hi Ts_ryan,

    Any update please let us know.

    Regards,

    Alan

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  2. Anonymous
    2017-05-05T13:29:31+00:00

    Hi Ts_ryan,

    Thanks for your update.

    Please change the From address to an Office 365 group’s email address in your Office 365 tenant and then send a test email to the Gmail account.

    In addition, please send us the SMTP Diag Tool. I’ve sent you a Private Message to collect it. You can access it via this link:

    https://answers.microsoft.com/en-us/privatemessages/list

    Regards,

    Barry

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  3. Anonymous
    2017-05-04T18:39:20+00:00

    Alan,

    I can do the same exact thing using telnet and SMTP commands. I just verified this...I connected to an Office 365 MX record on port 25, then used the commands to compose a message to a Gmail account. I received the message successfully in the Gmail account.

    So, it has nothing to do with SMTP Diag Tool...that's just a much easier/faster way of testing than using telnet and SMTP commands.

    It's most definitely not "good news" that Direct Send seems to not work the way Microsoft's documentation shows. It says it won't send to external recipients, but it does...unless I'm missing something here.

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  4. Anonymous
    2017-05-04T15:35:33+00:00

    Hi Ts_ryan,

    Thanks for your clarification. 

    It should be the tool's machanism. I will further check the tool. You may also test it via other device to see if ithe same situation. But, since you can send successfully, isn't it a good news.

    Regards,

    Alan

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  5. Anonymous
    2017-05-04T12:13:35+00:00

    I understand how direct send works. Can you please try to recreate the issue as I've described? Take any domain's Office 365 tenant MX record and try to use it to send mail from ******@thatdomain.com to a Gmail account. It sends successfully, which I don't believe should be allowed.

    Here's an example of the SMTP Diag Tool settings, the resulting log, and the message in Gmail. The O365 tenant for this MX record does NOT have a connector set up for the "SMTP Relay" method (which would make this work):

    (note that the MX record in the SMTP Server box has the beginning cut off in this screenshot)

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