Difference in note opened by user and by agent

Hi.

Maybe someone had similar problem or know where to look for answer.

I would like to know if is there any difference in note opened by agent and by user inside extension manager callback to EM_NSFNOTEOPEN(BYUNID).

I need to know this so I could display popup window when user opens mail and do not display it when agant is doing so.

Thanks in advance for any clue how to deal with this.