sendmail domain name

[Michael Scully]

Greetings:

	I use Hylafax at various Red Hat sites, and it allows the delivery
of email to the user to verify the fax delivery.  On top of that, we have
various cron processes report there success or failure by email.  These
Linux systems are internal boxes, not on public IPs, but the mail addresses
of the senders are to their normal ISP mailboxes.  At some sites, the ISP's
spam blocking disallows the mail to be received, because it can't do reverse
DNS on the domain name and verify the sender.  I've had the ISP's register
the public IP number with a domain name, and I've put this domain name in
both the /etc/hosts file and /etc/mail/local-host-names file.  But when I
look at the rejection notices, the outgoing mail is always shown as
"someuser"@localhost.

	There must be another piece of the puzzle I'm missing.  Also, what
do I do if I'd rather have Linux relay to another external mail server,
instead of its own SMTP service?

Scully