How mail routing works when both sender and receipient belongs to same server

Team,

i have 2 servers running both CAS and mailbox roles in single site.

User1 is on server1(ex01) and sending email to user2, who's also having his mailbox on server1(ex01). It gets delivered without any issues. But the email gets routed to ex02 server and come back to ex01 server to deliver the email.

My question here is why the email has to travel to ex02 server when both users are on same server(ex01).If there is any priority or some setting needs to be checked. please advice.

I haven't made any additional setting in the exchange org. it's just a plain default installation of 2013 RTM on 2008R2SP1 server.

Message details:

Received: from USAEXALL02.abcd.com (2002:82af:10d::82af:10d) byUSAEXALL01.abcd.com (2002:82af:10c::82af:10c) with Microsoft SMTP Server (TLS)
 id 15.0.516.32 via Mailbox Transport; Wed, 22 May 2013 12:12:40 -0700
Received: from USAEXALL01.abcd.com (2002:82af:10c::82af:10c) by USAEXALL02.abcd.com (2002:82af:10d::82af:10d) with Microsoft SMTP Server (TLS)
 id 15.0.516.32; Wed, 22 May 2013 12:12:18 -0700
Received: from USAEXALL01.abcd.com ([2002:82af:10c::82af:10c]) by USAEXALL01.abcd.com ([2002:82af:10c::82af:10c]) with mapi id 15.00.0516.029;
 Wed, 22 May 2013 12:12:18 -0700

Thanks,

Preni.

Thanks, Preni.