How to seup exchange/business units?

How to seup exchange/business units?

Hi,
 
Can anyone please explain how to setup the mail accounts for the different business units?
So far I have got business unit A with email address a@hoya.eu and business unit B with email address b b@hoya.eu.
 
If I send a request to business unit A, it arrives and I get confrimation. But if I send an mail to business unit B, nothing happens.
 
Am I doing something  wrong or did I miss something?
 
Thanks,
Allistair

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