Subscription for a web repository

Hi Experts ,

I am using EP 2004s , I have created a web repository and activated a subscription service for that.

Unfirtunately I am not able to receive any subscription notification emais , I can receive the subscription email for the repositories created inside the portal.

As per my understanding from sap help , for a web repository we should receive subscription notification emails once crawler detects the changes .

I have schedule the crawler accordingly so that it can detect the changes .

Can anybody through some light on , on which basis crawler considers that this document has been modified ?

Any advice , points are assured .

Thanks & Regards,

Amit Kade