Here are web sites for diagnosing DNS, Internet email, and other issues.
A very good place to test Internet email servers and servers in general exposed to the Internet at large.
DNSstuff is excellent for diagnosing DNS issues of all kinds. Most of its tools require a small subscription fee.
whatismyipaddress.com is very good for obtaining geographical and ISP information for an IP address.
https://www.testexchangeconnectivity.com/
is very good for testing Exchange WAN services, e.g., smartphone access, Outlook Anywhere.