You're right, strictly and academically speaking, but I wasn't wrong "in practice" if the relayed domain is known not to be reachable (dial up/off-line or occulted by firewall).
Len
=============
> Yeah, your Imail box is called 'bastion mail host' (aka, sacrifical goat)
> outside the firewall. To have Imail relay mail for the Exchange box:
>
> 1. in NT hosts file on the Imail box:
>
> exhangebox.com <ipaddress> (this maybe the external i/f of the
firewall)
>
> 2. in your DNS:
>
> exchangebox.com IN 1 MX imailbox.com
No, the host you're forwarding to should be the preferred MX record, with
your box as the secondary, thus yours will store the mail if the preferred
server isn't available;
IN MX 100 mail.exchangebox.com
IN MX 200 mail.imailbox.com
