I've run into some issues with a fresh Exchange 2016 install. Setup is:
Server 2012 R2 Std - DC
Server 2012 R2 Srd - Exchange (Hyper-V)
Send connector is configured to send mail through MX.
Older Netgear Prosafe Firewall - Port 25, 80, 110, 443, 587, and 2525 are open
At first I wasn't getting any mailflow in or out, but now I'm at least getting mail incoming after adding the IP of the server to the network bindings on the receive connectors. Outgoing used to just sit in the drafts (OWA) and do nothing prior to that change, but now it will get to Exchange and in the Queue viewer it shows "441 4.4.1 Error communicating with Host. Failed to connect."
I've researched this last night until I was blue in the face, I've recreated the send connector, I tried some port testing applications to verify port 25 was open, I have a single DNS server configured on the server's NIC, double checked the A record on the DC to make sure it had the correct IP for the exchange server, rebooted multiple times (transport services as well), and there's no antivirus on it.
I cannot telnet to any server (on port 25) from the exchange server, but port 25 is open. I'm assuming this is a DNS issue, but i'm not sure where else to look.
The other issue is Outlook won't connect to exchange either, but I'm assuming if there's a DNS issue somewhere it will fix both.
Thanks in advance!