This KB article contains a list of email deliverability tools and their functionality.
Wombatmail DNS Tools
URL: https://www.wombatmail.com/tools/
A quick page to check some basic DNS information for a domain and check for IP and Hostname reputation.
AboutMy.email
A quick page that gives you a one-time-use email address, and upon receipt of a message will give you information about the message and its delivery. See a sample report.
SPF Record Testing
The OG: https://www.kitterman.com/spf/validate.html
Prettier: https://dmarcian.com/spf-survey/
DMARC Policy Checking
https://dmarcian.com/dmarc-inspector