Why does it take FOREVER for Outlook to receive & refresh inbox???

We send ourselves emails to our Outlook account so they can be forwarded (pictures to attach, PO's from our corp ERP system, etc). When we cc our gmail or yahoo accounts, they are there ~instantly. When we email our corporate email in Outlook, IT CAN TAKE AN HOUR TO APPEAR!!!

We recently ported back to Outlook from the others, regretting it! Is there any trick to get our inbox to refresh? Have tried clicking to calendar, click back to email, there is no "Refresh" button like Yahoo email has....