Unfortunately, OJS only allows for a single email address per user account. However, depending on how much system-level access you have, it becomes possible to accomplish this sort of thing using your email server and a tool like procmail. If I was doing what you were attempting to do, I'd create a procmail rule that matched on an email subject, looking for the journal abbreviation (e.g. [MYJOURNAL]), and then forwarded the email to a different address.
Software Developer, Public Knowledge Project