Hi, due to some migration and transferring mail accounts from other domain and other mail system I am trying to find a solution how to route a messages between Exchange server, POP server and Lotus Domino server.

I am trying to set it up on Exchange server in Send connectors where I have an option of adding multiple servers to a single connector. Currently it set up so it routes all the emails for example: local.net domain to Domino server. I am considering adding a POP server to the list. Would that work, is Exchange "smart" enough to do the routing if email does not exist on one server to send it to another considering the fact that one is Lotus Domino and other is POP server.

Also, I know that Exchange has an option of flagging emails, would that solution be acceptable in this case since the emails that are going to POP server have different naming convention and I am able to distinguish them from others (they are still on the same domain as ones for Lotus Domino).

Is it possible to set up internal relaying so it flags some emails and points them to POP server and send others to Domino?

There's no way for the Exchange server to know which server hosts the mailbox except for an NDR but that's just going to result in a bounced message.

The best answer for you is to create separate address domains on the two other servers, and then create mail contacts in Exchange to point the users to their respective other domain address.  A side benefit of this approach is that you'll have a complete GAL.