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Recieving random '550.5.1.1 User Unknown' Delivery failures when sending to mailboxes in Exchange 2010 RRS feed

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    Hi,

     

    I receive random '550.5.1.1 mailbox unavailable' Delivery failures when sending to mailboxes in Exchange 2010

     

    related to anti spam??

     

    thanks

    Wednesday, November 16, 2011 8:07 AM

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    Hi

    Need some more information about the environment.

    What kind of mailflow is affected, only internal, only external, both?
    How many mailboxes are affected? Did they never received emails?

    Regards
    Pano

    Pano Boschung, PageUp AG
    Wednesday, November 16, 2011 12:33 PM
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    Hi,

     

    If there is edge transport server in your environment, maybe recipient filtering causes the problem.

     

    Understanding Recipient Filtering

     

    Best regards,

    Lisa

    Thursday, November 17, 2011 7:40 AM
    Moderator
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    I am sending to a distribution group and getting the same error (from Microsoft Outlook). However, when I use OWA the mails are delivered to all groups. Help please.

    Chibuking4Eva

    Wednesday, October 24, 2012 11:56 AM