Long delay in receiving external e-mails

Hello, I have setup Exchange 2013 with below scenario:

Domain Controller WS2012R2: "company.com", NIC1-Internal Network: 10.10.10.2. NIC2-External Network: 192.168.1.10 (NAT to Public IP)

Exchange Server 2013 WS2012R2: "company.com", NIC1-Internal Network: 10.10.10.3, NIC2-External Network: 192.168.1.11 (NAT to Public IP)

Mail-flow in working fine for internal network and I can send e-mails for external domains, However, it takes a few hours to receive anything from external domains. 

Can anyone please explain what can cause this issue?

And also, provide me a list of all necessary DNS records to set on my Public and Local DNS based on the scenario above. I want to make sure they are all added correctly.

Thanks!