Our Company has decided to set up some public-facing services using internal servers located in our server room. We currently own an internet domain called xyz.org. The internal server information and service information is listed below:

Mail-server 172.16.1.10
i. Hosting SMTP services for receiving inbound mail
ii. Hosting remote access to mail through the HTTPS protocol

Web-server 172.16.1.15
iii. Hosting web services using the HTTP protocol

a. How to make sure inbound mail from other Internet domains intended for the xyz.org domain can reach the mail server
b. How to make sure users can easily access e-mail securely remotely
c. How to make sure the our web server is easily accessible to the outside world

Hello

you can check all exchange services from outside with: https://testconnectivity.microsoft.com/

for email send/receive:
check send and receive connector
open firewall 25
check mx record, ptr record, A  record, cname
for user access email:
enable outlook anywhere, activesynch, and owa
open 443 port to mail server from internet.
set A record and cname and check certificate to contain domain name like /owa.xyz.org, smtp.xyz.org, eas.xyz.org, mail.xyz.org, internal.domain.local ........../
set all external url
and check all services with https://testconnectivity.microsoft.com/ if test run faild need check again your settings and run again tes

Thanks Sneff_Gabor...