Hi Eugen,

I understand your problem and I see your point but what you must understand is that you are asking for something that has NOT been sent to be highlighted, as far as I know there is no way to do this as yet although what you have asked for is would be a great feature in outlook.
The only thing I know of is the conversation mode in outlook 2010 that keeps all mails with the same header (subject) bunched together, having said that conversation mode is only mails that have been sent.
You can check this link fom Microsoft for more on the coversation mode.....but I dont know of anyway to highlight a non-response.
You said you are a manager....does your IT team have any suggestions?

Good luck and if you get an answer please post it here so we can see it...thanks