Riddle me this batman. I have an isolated lab environment which doesn't have internet access, but does have Exchange, Domain Controllers, and client machines running Outlook. When opening Outlook in this isolated environment, it takes about 40 seconds for Outlook to find and connect to Exchange. If I jump into the lab firewall and give said client internet access, this problem goes away. Outlook client connects to isolated Exchange server instantly.
Exchange 2016 on-prem and Windows 10. Outlook version 2013.