Need to configure relay mailboxes under Sendmail

Hello Experts !

I have the following configuration:

1- RH Linux server configured with Sendmail to host email accounts from the company's foreign domain.
2- Fetchmail as POP3 client to download messages from the company's foreign domain into the local Sendmail (Linux) accounts.
3- Sendmail as MTA to send messages inside the local network and to the internet as well.

What happens ? Everything works fine: messages are downloaded and distributed to the Linux accounts. Users interact with internal Linux server to download or send email from their mail client. Messages to outside domains are queued and sent by Sendmail. The problem is that some mailboxes are for the company's remote users that do not have a Linux account. Those messages bounce back when an internal user sends it with an unknown mailbox message. Of course, this happens because the account does not exist on the Linux server.

Question is, how can I configure relaying mailboxes to forward those messages to an external MTA so they can reach the server hosting the company's domain ? I tried using Smart host bit it didn't work.
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You could set up mailboxes for the remote users on the RH box and use .forward files to send them on to their remote accounts.

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You can set up a virtual domain for those individuals that are not on the host in question:

or another alternative that is really quick and easy to set up is Xmail:

For this you would set up the server so that all email accounts are 'virtual'. You can have multiple virtual domains with this server very easily as part of the basic install - its main strength. After that, all users would 'fetchmail' their mail from the Xmail server.
agubairaAuthor Commented:
I will be trying both solutions next week. Sorry for the delay.
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