Bind & Sendmail

[Sean]

Greetings,

I reviewed the archives before posting this message and have not encountered anything similar, so here I go:

I have set up an intranet within a small office environment. There are 15 users, 5 of which access the Internet via dial-up modem. For convenience, I set up DNS on the Linux server with the domain name intra.net which, of course, does not exist. I set the forwarders as the ISP's DNS addresses. This has worked quite well.
Users can access the Linux server by entering http://linux.intra.net into their web browsers. The 5 dial-up users can access the internet.
Now, however, I would like to implement fetchamail and sendmail to allow all users to have, at least, local mail. The problem I am encountering is that when sendmail communicates with the ISP's smtp server, it returns back the error message that the domain "intra.net" must exist.
Is there a way to correct other than registering a domain name or sacrificing DNS?

Any info will be greatly appreciated.

Thanks,
Sean.