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Our custom 404 page sends us Emails to notify us of broken links. We've been lately getting emails with such a missing page:

http://domain.com/undefined

However, no log entries (IIS) exist on that time with such a request. Further - no log entries exist with the requesting IP (also sent in the email).

What can this mean?

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Just to clarify... no match in the access log (or error log)?! Presumably your custom 404 page is not accessible directly over HTTP? –  w3d Sep 9 '12 at 10:25
    
@w3d - Access log. Usually these requests are logged as code 200 because they end up finding a page (our 404). But here there is no log of the request. –  JNF Sep 10 '12 at 6:42
    
The IP address in the email... does a reverse lookup reveal anything? Does the country of origin suggest spam? Is it local? Could this be a real visitor? –  w3d Sep 10 '12 at 7:09
    
@w3d, It's mostly from our country, but not only (most our traffic is), and it's scattered all over. It arrives from different ISPs as well. –  JNF Sep 10 '12 at 8:36
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1 Answer

I have encountered similar things in IIS before, what happens (I think) is that IIS has utilities to check syntax errors or compatibility issues within files that it views as executable. Regardless why it does it, the server will parse this file. Because it effectively renders a page, your mailing functions (or any other functions for that matter) will fire. IIS won't generate a log entry because it isn't a "true" request, it is just the server performing some sort of maintenance or run-through.

I am not 100% sure why IIS does this, whether it is a syntax thing or not, but I know that I have had a few pages generate database content with no record of logs or any other user tracking.

Here is a configuration link that might be helpful: MSDN Custom Error Pages

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Your saying there wasn't actually an external request to the above URL? –  JNF Sep 19 '12 at 5:25
    
right, it seems that IIS internally runs some of it's scripts for some reason. It would not have loaded the url because it will run scripts internally. At least, that is what it seems like. –  Ryan Sep 19 '12 at 17:56
    
This seems really really weird. –  JNF Sep 20 '12 at 5:21
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