Solution : https://service.sap.com/sap/support/notes/1171502 (SAP Service marketplace login required)
Summary : 
      
Key words : 
parameter  icm/smtp/close_conn_after_quit = 1this parameter, smtp servers close, symptom errors occur, sending e-mails, resend e-mails, internet communication manager, domino server reason, 640 143700 73in versions higher, tcp connection immediately, 1168]smtp smtpclientclose
Related Notes : 
       
| 851852 | ICM Patch Collection (7.00) | 
| 698017 | ICM Patch Collection (6.40) |