Slow Receiving Emails

I have just upgraded our previous Exchange 2010 server to Exchange 2013.

Using three seperate accounts I am currently having problems receiving emails on my exchange server. Using different accounts I am getting different results;

Office 365 Account: Receive the email after 14 hours

Gmail Account: Receive the email within 3-4 hours

From internal account: Receive the email within seconds.

I can send emails and it takes various periods of time to receive the email on the other end (normally within the hour).

This is really annoying me as it use to work on Exchange 2010 and does work in a Lab environment.

Cheers,

Ben