DNS Tools

DNS Configuration Check

https://intodns.com/

The Defacto DNS configuration check and guidelines.

IP Addresses

ifconfig.co

https://ifconfig.co

Determine your IP by browser or command line

Mail Tools

OVH Mail Migration

https://omm.ovh.net

Migrate Email between IMAP/Exchange and other formats

MX ToolBox

https://mxtoolbox.com

Plethora of Different Tools Useful for Mail Diagnosis

What Is My IP Address

IP Black List Check

https://whatismyipaddress.com/blacklist-check

Proxy Check

https://whatismyipaddress.com/proxy-check