Mail is Slow between Exchange 2010 and 2013 During Co-Existance Transition

Hello,

I recently migrated from a single Exchange 2003 server to a single Exchange 2010 server

I am now trying to Migrate from Exchange 2010 to Exchange 2013.

I have a test user on Exchange 2013, and Internet Mail works fine and quickly both inbound and outbound.

However, when I try and send between a 2010 user to my 2013 user, delivery takes around 10 minutes.

On the 2013 server I see health check messages, and my 2010 user's message stuck in retry status. The messages eventually clear and the mail is delivered. Any ideas what is causing this delay?

In terms of connectors I have all the defaults. And I created 1 for internal relays from devices. Which works fine.

I have two Exchange 2013 servers configured in a DAG, but I don't have a load balance in place as of yet. So only server 1 is being accessed as the CAS.

Thanks