Messages from Yahoo are hitting 'Mail Policy Violation'

Messages from Yahoo are hitting 'Mail Policy Violation'

Dear zMail Team,

A few messages from Yahoo domain are encountering ' MailPolicy violation Error delivering to mailboxes'. What does this cryptic error message indicate? Can you be more elaborate on the messages that you communicate to peer SMTP servers?

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Deepak Vasudevan
http://thamizhththendral.blogspot.com/