Here is the scenario:
SBS 2003 and the internal domain is MyDomainServer.Local and the public domain is MyDomain.com. There are 10 users all of which have domain accounts with the corresponding SMTP addresses…user@MyDomainServer.Local and users@MyDomain.com. Only 5 of these users actually log on to the SBS domain and Outlook setup for Exchange the other half are peer to peer and get their email from the ISP (POP3) which is still hosting the mail server (MX record) for MyDomain.com. The Exchange users are setup to have their POP3 mail pulled from the ISP (same username) via the POP3 Connector and delivered to their Exchange mailbox. A Smart Host (the ISP’s SMTP server) is configured on the “SmallBusinessSMTPConnector” to deliver mail to the outside world when sent from the Exchange clients.
When a user who is on the domain, user1@MyDomain.com sends mail to a user not on the domain, user2@MyDomain.com, user2 does not get the message (in ISP POP3 mailbox) because it never leaves the SBS server and is delivered to the Exchange Mailbox. Furthermore there are some email accounts hosted at the ISP, others@MyDomain.com, that are not associated to any user accounts on the SBS server and when mail is sent from inside the domain they are not delivered but a system admin error is returned. (I forget the exact message)
MyDomain.com – ISP MyDomain.com – SBS2003
User1@MyDomain.com <- User1@MyDomain.com (delivered to Exch Account)
User2@MyDomain.com <- User2@MyDomain.com (delivered to Exch Account)
Other Accounts at ISP only
User3@MyDomain.com (will not sent out from SBS2003 - error) <- User1@MyDomain.com
User4@MyDomain.com (will not sent out from SBS2003 - error) <- User2@MyDomain.com
The client wants to have some users not on the Domain. They do not want to let the Exchange server be the mail server for MyDomain.com.
From what I can tell from my research is that this is Exchange behavior is by design. It believes that it is the only MyDomain.com there is and would have to be tricked into making this scenario work.
What I am looking for is “Best Practice” not a hack or a trick.
Experts only please advise.