How does Exchange 2010 prevent auto-reply loop

I admit I'm no expert at this, but why it would do that is beyond me. I haven't had an Exchange installation do that as far as I recall, it will send the auto-reply once per sender. However, the end-user could with Outlook set up a manual rule that does that (or perhaps this Outlook 2000 KB about orphaned rules causing this is helpful).

Exchange can also be configured to not allow auto-reply outside the organisation at all regardless of user-configured rules, which may be seen as a good practice.

If I'm not mistaken, in order for this to be a server side rule, you'll have to create a custom form and publish it to the Exchange Organizational forms library, then set up the rule in Outlook to respond to the messages that meet the criteria with the custom form that you published to the Exchange Organizational forms library. The following links may be helpful:

http://www.outlookcode.com/article.aspx?id=34

http://support.microsoft.com/?kbid=244591