Email configuration check
Whether a domain can send mail that arrives, and whether anyone else can send as it.
What gets checked
DNS Records
A, AAAA, MX, NS, CNAME and other records held for the domain
TXT Records
TXT records, including domain verification and policy entries
Email Configuration
MX, SPF, DKIM and DMARC records for sending and receiving mail
Block Detection
Whether privacy, malware and parental-control resolvers block the site
What this tells you
Deliverability comes down to records the domain publishes. MX says where mail goes. SPF, DKIM and DMARC are how a receiving server decides a message really came from you.
Get them wrong and two things happen at once: your own mail starts landing in spam, and forging your address becomes trivial.