How to configure exchange for access from outside?

Question

System administration

Yes:
MS Exchange 2016 CU11
AD: bn.local
WEB: bestname.com
External access is configured on the server at ms.bestname.com. I can log into OWA and ECP and send and receive emails.
I can't connect any program to receive mail.
Help me understand what's going on.

Answer 1

Are ports 143/tcp, 993/tcp open outside?

Answer 2

Outlook is a standard client for Exchange, since version 2013 client applications connect using the Outlook Anywhere protocol (the marketing name is RPC-over-HTTP, which wraps MAPI into RPC, and RPC into HTTPS, in 2016 there was still a new protocol, but that's another story. ). Those. in this situation, only an open port 443 is required.
Since you can log into OWA/ECP, this condition is met.
Now you need to configure the Exchange 2016 Web Services - in your name (ExternalURL).
The best option is to use Split-Brain DNS in this case, and set the ExternalURL & InternalURL the same as the one you provided ms.bestname.com.
Then the user will still be sitting inside the corp. environment or opened mail from home - it will connect seamlessly.
Another plus is the use of one certificate for external-internal users.
This is a fishing rod for you -) Successful fishing =)