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Incoming SMTP – 530 5.7.1 errors
By default, Exchange 2007 requires authentication for incoming SMTP sessions and this may cause incoming e-mail to be rejected with 530 5.7.1 Client was not authenticated (in reply to MAIL FROM command)). The fix is simple: in the Exchange Management Console, click on Server Configuration, Hub Transport and double-click on the default receive connector to view its properties. Click the Permissions Group tab, enable the Anonymous Users option and save the changes.