Solution : https://service.sap.com/sap/support/notes/1072558 (SAP Service marketplace login required)
Key words : 
configuration parameter 'send firefightid login notification', symptom superuser privilege management, define external email address, define parameter settings, superuser privilege management, define rfc destination, transaction /virsa/vfat, spm configuration guide, service type userid, spm rfc call
Related Notes : 
       
| 1609074 | FAQ: Firefighter Login Notification email scheduling | 
| 1350046 | Blank Owner in the Firefighter to Firefighter ID Assignment | 
| 1289579 | Firefighter Owner additional authorization for Role based FF | 
| 1263952 | Superuser Privilege Management Configuration Change Log | 
| 1170009 | FF 5.2 Migration Utility not updating Descriptions | 
| 1058596 | Firefighter Controller Additional Authorization | 
| 1049720 | Getting the error in the FF "No valid records to maintain" | 
| 1048325 | Firefighter 5.2- Missing buttons in Firefighter Dashboard |