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If you configure Exchange Server 2007 for auto-reply on a public address, and the reply is sent to an address that also has auto-reply or out-of-office-auto-reply, then Exchange Server will receive a new message, same from-address, and will again send an auto-reply. This can go on forever and can potentially lead to a DoS situation.

How can I prevent multiple sending of auto-reply to the same address, preferably in a given timeframe (to prevent legitimate multiple mails to be treated incorrectly), using Exchange Server 2007?

Our XS hosting provider says it cannot be done, but that strikes me as odd.

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I'm pretty sure that Exchange with the default configuration does send only one message per email address. Hmm... – splattne Jan 8 '10 at 12:21
For out-of-office, yes. For auto-reply, no. – Abel Jan 8 '10 at 12:29

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.

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The auto-reply is on a public box, saying something like "thanks for your mail, we'll be answering your query shortly". If you say the auto-reply should not re-reply to an out-of-office message, then something else is up. – Abel Jan 8 '10 at 12:13
No the Out Of Office rule will only do it once, manually configured rules outside of the OO Assistant scope however do that and are therefore not recommended to use at all. Normally you'd need a third-party responder or some tool hooked to Exchange events to handle this - or use a utility to move an OOA rule from an account mailbox to wherever you have the auto-reply (public folder?) – Oskar Duveborn Jan 8 '10 at 13:51

Out of office will only answer once. If you do an Auto-reply, you could end up with an mail storm situation like you are describing.

In your auto-reply logic - be it a vbscript or rule - try to add an exclusion for a subject with "RE: " in it. This would prevent the auto-reply from going out on an incoming reply to any message you send out.

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up vote 0 down vote accepted

Eventually, the solution proved to be rather trivial: add the Precedence: BULK header to the e-mail (as is common with news letters and such) and replies will not end up in a mail-loop, because they are ignored.

I found this in the general guideline of mail on bulkmail.

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