External DNS Diagnostic Tools
Google Admin Toolbox Dig
Google Admin Toolbox Dig is an online way to run dig queries, useful for troubleshooting DNS and checking resolution.
Link: https://toolbox.googleapps.com/apps/dig/
IntoDNS
IntoDNS provides health/config reports and suggestions.
Link: https://intodns.com/
ViewDNS
ViewDNS is a collection of lookup and troubleshooting tools.
Link: https://viewdns.info/
WhatsMyDNS
WhatsMyDNS is a global propagation checker, useful to compare results across locations.
Link: https://www.whatsmydns.net/