The messages will spread between the servers.
Reading from a mailbox is ultimatly done using a SYS$QIO(w) call,
perhaps called directly, through RMS, and/or a language IO function.
As its name implies, this system service performs QUEUED IOs.
Assuming NO message in the mailbox, and not using the IO$M_NOW
modifier, all the read QIOs from all the servers will be put in QUEUE.
The first message to come in will satify the first QIO and only that
first one. Next message goes to the next and so on... FIFO.
>I do not have access to the source for the Server so
>I cannot rewrite its front end.
Notwithstanding the above, runnning multiple copies of the server
_might_ still fail IFF that server happens to use the WRITE-ATTENTION-
AST mechanism and happens not to be prepared for the case where no
(more) message is found when the actual read QIO is performed.
One could argue that an not ready for this is badly broken but hey...