Sendmail masquerading

I wan't to mail outside my LAN - to the Internet!
But my ISP claims that my "From:" is not of an known domain. Of course
it isn't, it's my local domain.
And therefore I have tried to use the Sendmails "MASQURADE" functions.
Without any success.
I've done it like this:

MASQUERADE_AS(My_ISP_DOMAIN)dnl
MASQURADE_DOMAIN(localhost)
MASQURADE_DOMAIN(localhost.domain)

Now I begin to believe that I totaly missunderstood the use of
MASQUERADE. Is there any other solution that can work or have I to give
up sendmail.

I'm using tripwire and want it to report to an address outside my LAN.
Otherwise it's easy e.g. with Pine you can set the From-address to
whatever you like and then it work's. But in the case of tripwire I
don't know any other way.

>
> MASQUERADE_AS(My_ISP_DOMAIN)dnl
> MASQURADE_DOMAIN(localhost)
> MASQURADE_DOMAIN(localhost.domain)

I find sendmail to be very difficult, but I managed to get my machine to
send outgoing mail just yesterday. Do you need to include your email
account with "My_ISP_DOMAIN"? That's what I did.

This is what I did


define(`SMART_HOST', `[smtp.east.cox.net]')
MASQUERADE_AS((E-Mail Removed))
FEATURE(masquerade_envelope)
MASQUERADE_DOMAIN('smooch.turgidson.com')
FEATURE(masquerade_envelope)
FEATURE(`genericstable')
GENERICS_DOMAIN_FILE(`/etc/mail/generics-domains')

Then, create these 2 files:

/etc/mail$ cat genericstable
(E-Mail Removed) (E-Mail Removed)

/etc/mail$ cat generics-domains
smooch.turgidson.com