I suspect that programs such as Thunderbird, Eudora, and Outlook Express that submit e-mails through a SMTP link do just copy the "From: " line in the header. But if you use something like mutt that uses sendmail-compatible message submission, your MTA will [1] use your username and its idea of what the local host is called. And I haven't always thought to check that it's using westexe.demon.co.uk, not localhost.localdomain or my internal name for the computer.
At least posting to the Fedora list keeps my mail setup working properly!
I've learnt that lesson now. Time to go make more mistakes...
James.
[1] Unless I'm missing a config option somewhere, which is quite possible.
If your machine tends to choose different hostnames for itself from time to time, e.g. because you connect it to different networks, you can "fix" it for sendmail by using:
define(`confDOMAIN_NAME', `my.full.host.name')dnl
in your sendmail.mc file.
Also see "MASQUERADING AND RELAYING" in /usr/share/sendmail-cf/README and the section on "genericstable" if you want to rewrite outgoing usernames as well as domain names.
Paul.
