If a computer is not managed in Enterprise Console, it will not act as a message relay server.
Even if a computer has not been converted to a message relay server, any messages will still be forwarded to Enterprise Console and the workstations. However, this is only true if the unconverted computer is a managed computer.
Once the unmanaged computer has become managed, forwarding will work correctly.
Note: Even if a computer is present in Enterprise Console, this does not mean that it is managed. No messages will be forwarded from such a computer.