subscribing calendar events without using impersonate or delgae access

Hi,

Is there any way to subscribe calender/mailbox event for each outlook user without using impersonate or delegate access approch. 

if yes, please share how it can be done, as i found only impersonate approach or delegate acess.

if no, please share the best possible solution to subscribe calendar events for each outlook user.

I am new to exchange server developement, so do not know much.

Thanks

Nitin