原因是缺省系统之允许回应内部邮件。
参见：http://www.adminspy.com/Windows-Tips/Microsoft-Outlook-Out-Of-Office-doesnt-work.html
If your Out of Office does work internally but not externally then follow the instructions below
If you use the Out Of Office Assistant and turn on the out-of-office reply, the internal senders (on the local network) receive the automatic reply message, but external senders (on the Internet) may not receive the automatic reply.
PROBLEM
By default, the out-of-office reply to Internet recipients is turned off. Many administrators do not allow out-of-office replies to be sent outside the Exchange Server organization, so that unauthorized people do not know when users are out of the office.
RESOLUTION
To turn on out-of-office replies to the Internet, follow these steps:
On the Exchange server, start Exchange System Manager.
Go to Global Settings, and then click Internet Message Formats.
In the Details pane, right-click on your domain name, and then click Properties. The default SMTP domain is "*".
In the Properties dialog box, click the Advanced tab, and then click to select the Allow out of office responses check box. This turns on out-of-office responses to the Internet for the selected domain.
This was tested no Windows 2003 server with Exchange SP1 installed
You may need to restart the Simple Mail Transfer Protocol (SMTP) and Microsoft Exchange Routing Engine services
另外一个可能性：启用了上面的设置，但还不管用，可能是return地址没有。如下：
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I think i found the problem, look at the internet header from the email and you will see that there is no return path<>
the cause can be that your email provider removes the return path and the exchange server cannot send a OoO reply. I opened a ticket at our email provider and hope for an answer. will be continued.... |
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