I'm required to setup an exchange 2013, with a few particular rules, for instance many of the hosted mailboxes in the local databases are not allowed to send or receive messages to each other. Also for a few clients that use owa I would like to relay the messages to a external smtp appliance that contains filter rules. 
Is this possible in exchange 2013, to route internal email to a smtp appliance even if the mailboxes are in the same organization? 
How can this be accomplished? 
Currently the mailboxes are in a mail appliance and the goal is to move them to an exchange environment as it is more supportable and escalable than the applian

I can't think of any way to accomplish this.

Take a look at internal relay domains section here: https://technet.microsoft.com/en-us/library/bb124423(v=exchg.150).aspx

You should be able to have some mailboxes on Exchange and some on your mail appliance, all using the same domain name. Exchange should be able to deliver emails to mailboxes on each messaging system by using internal relay domains.

Thanks for the information, to be more specific , I have a few users that only use OWA, so I will need to make owa going  thru my email appliance , because I have all the rules and statistics in the appliance, so I need to find a way to send owa to the appliance first.

If you want the users on Exchange to have their internal email routed through your mail appliance then I don't think this is possible or worth trying. There may be an option by setting up a journal mailbox on your mail appliance then setting up contact to be used for journalling on Exchange so there is a record of the email going through your mail appliance and use this for stats. Another option could be to set up a hub transport rule to forward or bcc emails to another recipient which is on your mail appliance. 

These options are quite messy so the best option would be to set up collection of stats using message tracking logs and the filter rules (hub transport rules) on the Exchange server.

External email filtering and stats is not a problem as you could probably get email routing through the email appliance. 

An internal relay domain is what you need when you have some mailboxes on a non-Exchange server and some on Exchange. 

Let me know if this is helpful.