nicholas@mordor:~/mail$ 
nicholas@mordor:~/mail$ ss -tlpn sport 25
State                   Recv-Q                  Send-Q                                   Local Address:Port                                    Peer Address:Port                  Process                  
LISTEN                  0                       100                                          127.0.0.1:25                                           0.0.0.0:*                                              
LISTEN                  0                       100                                              [::1]:25                                              [::]:*                                              
nicholas@mordor:~/mail$