Mine

postconf -n:

command_directory = /usr/sbin
config_directory = /etc/postfix
daemon_directory = /usr/libexec/postfix
debug_peer_level = 2
html_directory = /usr/share/doc/html/postfix
inet_interfaces = all
inet_protocols = all
mail_owner = postfix
mail_spool_directory = /var/mail
mailq_path = /usr/bin/mailq
manpage_directory = /usr/share/man
mydestination = myexternaldomain.com, $myhostname, localhost.$mydomain, localhost
myhostname = altair.home
myorigin = /etc/mailname
newaliases_path = /usr/bin/newaliases
queue_directory = /var/spool/postfix
readme_directory = /usr/share/examples/postfix
sample_directory = /usr/share/examples/postfix
sendmail_path = /usr/sbin/sendmail
setgid_group = maildrop
unknown_local_recipient_reject_code = 550

/etc/mailname:
myexternaldomain.com

hostname of machine:
altair.home