Exchange 2010 NDR “554 5.1.0 Sender denied”

I have came across this issue quite a lot recently , where an external user is unable to send a mail to a specific users mailbox inside your exchange environment.

The first thing i did was check the anti-spam agents on the Edge Server and there was nothing denying a specific external user in any of the filters and as it was only one specific user inside the whole internal organisation who couldn’t receive mail from the external sender i turned my intentions elsewhere.

I then explored the avenue of Safelist aggregation. Safelist aggregation basically gets information out of a users Mailbox of the Safe Recipients Lists, Safe Senders Lists, Blocked Senders Lists and contact data and passes this information onto the anti-spam agents on the edge server.

The user then checked there blocked senders in outlook to find the external users email address stored in there, so they just took this out and the “554 5.1.0 Sender denied” NDR for the external user disappeared and the user received the mail Smile

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  1. Chris

    Thanks for the post, Daniel! It got me in the right direction for fixing this issue. We did what you suggested (removing the email address from the block list and adding them to the safe senders list), but that didn’t quite fix it for us. I still had to go in and force Exchange to update the safe senders list for my user. The EMS command for this is:

    Update-Safelist -Identity -Type SafeSenders

    That fixed it for me!

  2. Exhange2010

    Thank you!!!

  3. Matt

    Saved me lots of time…Thank you!

  4. ken

    This was a life saver. Saved me tons of time with a client. Gracias

  5. caren

    I am not sure if the block is in MY e-mail receiver, or intended RECIPIENT’S e-mail receiver. Since e-mail is the only way we communicate, how do I find out, if my e-mail is blocked this way? The receiver is NOT on MY blocked list, is the INTERNET doing this, or is the receiver? How do I find out?

    And why DOES the internet sometimes do this? I myself sometimes find a trusted source “blocked” into my junk file, why does this happen? Can a hacker do this TO you?

  6. Adrian

    That did the trick, thanks!

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