sendmail, 4th Edition

-d0.20

Print network address of each interface Debug command-line switch

When sendmail scans the network hardware to find other names for the local host, it uses only those names that are new. Each new name was printed by the -d0.4 debugging switch described earlier. To see every name that sendmail finds, new and old alike, use the -d0.20 debugging switch:

128.32.201.55                                        ← already found
127.0.0.1                                            ← found new
        a.k.a.: [127.0.0.1]