cannot open encrypted *.eml files - [Portions of this MIME document are encrypted with a Notes certificate and cannot be read.]

The following message appears when opening an *.eml file, which was saved before from an encrypted email.
                                                                                              
[Portions of this MIME document are encrypted with a Notes certificate and cannot be read.]                                                   
                                                                       
Steps to reproduce:                                                    
                                                                       
1. open a new memo                                               
2. send memo to yourself or another recipient with encryption flag     
3. open the email (you will see everything)                            
4. save the email as *.eml file (File >> Save as)                      
5. open the *.eml file                                                 
6. the error occurs (in standard and basic configuration)             

Need some solution to save the encrypted email and shared with other users.