451 VS* Excessive unknown recipients - possible Open Relay

Discussion in 'Mail Server Support' started by popowich, Aug 18, 2009.

  1. popowich

    popowich EQ Forum Admin Staff Member

    Aug 12, 2008
    Likes Received:
    According to Yahoo Help :

    This error indicates that Yahoo! Mail has been receiving a substantial amount of emails from your server that are addressed to inactive or invalid recipients. This can signify that your mailing list, if you have one, may need updating so that email addresses that are no longer valid be permanently removed. It can also mean that a machine on your network may be compromised and is sending out spam directed to invalid Yahoo! accounts.

    Please see this page to view best practices relating to mailing lists, while information on securing your machine is available here.

    Note: If you are not the administrator of the mail server in question, please contact the administrator directly with the error message you are receiving.

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