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With internal recipients everything works great. Exchange 2010 Out of office mails are sent and received. For external recipients, out of office mails are sent OK but they are not accepted by the external recipients :

said: 550 Requested action not taken: mailbox unavailable (in reply to MAIL FROM command))

When I bypass the postfix smart host out of office mails are received by external recipients but when I go trough the postfix smart host it doesn't work.

Here is a diagram : Out of office mails are refused:

  • Incomming mails: Internet -> Postfix -> Exchange 2010
  • Outgoing mails: Internet <- Postfix <- Exchange 2010

Out of office mails are accepted:

  • Incomming mails: Internet -> Postfix -> Exchange 2010
  • Outgoing mails: Internet <- Exchange 2010

Do you know why postfix is interfering and preventing out of office mails to be refused (550 mailbox unavailable)?

Do you know if it is dangerous to go out directly without any smart host?

Thank you in advance

  • According to your description, it's not an Exchange issue, you can contact the supplier of your postfix smart host to feedback your problem. In addition, you can safely go out directly without any smart host. – joyceshen May 22 at 8:39
  • Thank you. Do you have any idea why postfix prevent my Out Of Office mails from being accepted by Gmail, Hotmail, Yahoo etc.? Saddly, the supplier doesn't work here anymore. And I don't know why with the smart host it doesn't work. Secondly, if I by-pass the smart host for outgoing mails it doesn't work anymore for several mails: Error 1: temporarily deferred due to user complaints - 4.16.55.1 Error 2: Client host rejected: cannot find your reverse hostname – Philipili May 22 at 12:20
  • Have you checked the blacklist of your ip address? Also this case for your reference:community.spiceworks.com/topic/405712-client-host-rejected – joyceshen May 24 at 8:13

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