Coexistance Between Lotus Notes and Exchange 2003 - Create a new appointment

Hello,

One of our customer encounter problems during the creation and validation of an appointment between an Exchange user and Notes user.

1. The Exchange user create an appointment involving a Notes user
2. The Notes user receives the request for appointment and valid it. An email confirmation is sent to the exchange user.
3. The Exchange user not receiving the  mail confirmation.
4. The Notes user receives an email of non-delivery.

Here is the mail non-delivery:


Notice of non-distribution
                                                                         
Your Accepted: COSI
Message:
                                                                         
Avis de non-distribution
                                                                         
You                                                      
message :    Accepted : COSI                                                            
                                                                         
Not sent to     IMCEANOTES-Toto+2ELEGRAND+40Exchange@cccc.ch                
 :                                                                                                                                            
                                                                         
Motif :     550 Recipient unknown


  Strange how the address of the Exchange user appears: IMCEANOTES-Toto 2 ELEGRAND 40 Exchange@cccc.ch


Could you help me? I am very annoyed with this problem.

Thank you in advance.