Just for the record.....
I am happy to announce that there is a solution.
Ok so lets say that the remote head office (site A) has a domain name of contoso.com and you need your clients to use the same for e-mail at your office (site B).
Have an e-mail relay account created at site A (pop3 account)
Then on your exchange 2007 at site B do the following:
in exchange 2007 under orgarnization configuration, Hub Transport...... create a new Accepted domain using site A`s domain name (ie: contoso.com) set it as an internal relay (also set it to default)
then create a new e-mail address policy to be applied to all accounts ... also configured as contoso.com (this will change your users e-mail address`s from @siteb.comtoso.com to @contoso.com (make sure it has a priority of 1)
then you need to create 2 SMTP Send Connectors the first one`s address space must be contoso.com (no astrix`s or dots)
Under network select ...route through the following smart host and configure the account details for the relay you had setup at site A in the beginning of this document
Then create another SMTP Send Connector but under the address space only put in an asterix (*) and setup your network tab the same as the first connector (smart host connecting to Site A`s Host name with username and password)
The first SMTP connector will push all contoso mails that are not configured on your exchange to Site A for resolution
the Second will handle all other domains
Dont make the mistake i made.... local delivery is not disabled by doing this so any mailbox setup in your exchange will still get mail locally if the mailbox does not exist .........THEN only will it look externally. (also make sure that only local users are in your global address list)
I deleted all other Accepted domains and all other smtp Send connectors that were there by default
lastly what i did was the other 2 e-mail address policies.... i modified them to both be contoso.com not siteb-contoso.com or anything else.
Also i did not bother with an edge server ...etc... as i didn`t need it.
you need to reset your exchange services and all shoud be working.
for the record... i thought my self signed cerficate that i created was playing a part of my mail not sending correctly....... well it DOES NOT make any difference at this point ...........its all about your accepted domain, send connectors, e-mail address policy and your smart host
if you have any hassles let me know
also here is another reference that i used.
best of luck guys.