I found one tutorial on setting up sendmail that says that in the /etc/hosts file, "The entry for 127.0.0.1 must always be followed by the fully qualified domain name (FQDN) of the server." Like so:
127.0.0.1 bigboy.my-site.com localhost.localdomain localhost bigboy
(This tutorial is here).
However, I can't find anyone else suggesting something like that. instead most people seem to put some combination of localhost and localdomain.localhost after 127.0.0.1, and then some variant of the fully qualified domain name after the public ip address.
What is the correct way?