Exchange 2013 Outlook Anywhere (RPC over HTTP) not working
Last Updated: 8/1/17note: this is a very quick post. hopefully I will have time to add more later. We had to open a Microsoft ticket to resolve this, but ended up finding the solution ourselves while the ticket was open.
Symptoms
Outlook clients connect fine internally, but over the internet they cannot connecting using RPC/HTTP or MAPI/HTTP.
I was researching all sorts of error messages that got me no where: MAPI TCP 6001, TCP 6002, rpcProxy IIS errors, etc....
Cause
We host our own DNS server that serves both interal and external requests. This apparently confuses Outlook clients trying to use Outlook anywhere. I think having our internal server names resolve via DNS was confusing Outlook. We blocked these requests at the firewall, but the very act of a successfuly DNS request was enought to confuse Outlook.
Solution
Enable MAPI/HTTP, because it is better than Outlook Anywhere (RPC/HTTP) and don't publish all your internal DNS records externally. Implement split DNS.
*This was already the best practice for a million reasons, but we have always had one DNS zone published externally and internally for over a decade. Not any more.
