Copy /usr/lib/sendmail.main.cf to /etc/sendmail.cf.
Edit the new /etc/sendmail.cf and make the following changes:
Comment out the line Dj$m in the local info section
near the top of the file (that is, change Dj$m to #Dj$m).
Uncomment the line 4 lines below that says #Dj$w to make it
Dj$w.
Change DMsmartuucp to DMddn.
Change DRddn-gateway to DRrelay.net.provider and
CRddn-gateway to CRrelay.net.provider.
Add a new line just after the last two changes that is
Cw gboxname gbox-othername (use the hostnames assigned
to the G Box's two network interfaces).
Locate the two example lines which contain the word Podunk
and use as a model to define your local domain name.
Edit your /etc/rc.local script to specify your hostname as the
fully qualified hostname (i.e., add a line, just before the line which
begins with ifconfig which says hostname hostname.your.domain
substituting the full hostname of your system, with your Internet
domain name appended).
This runs sendmail in verbose mode, and you can watch the
name resolution and SMTP conversation in progress; it sends
an empty mail message to the address specified.