I have been trying to send email on one of my linux workstations, but the sender address has the host name of my machine. This causes problems because the host name is not a publicly resolvable name. I found the solution on this page.
Create a file /etc/mail/genericstable
Put the following in it:
makemap hash /etc/mail/genericstable < /etc/mail/genericstable
Add the following to /etc/mail/sendmail.mc
m4 /etc/mail/sendmail.mc > /etc/sendmail.cf
In postfix, all you need to do is specify
myorigin = $mydomain
in the main.cf file.