Connect to a domain's mail server and read the SMTP banner.
One report for the whole domain: MX, SPF, DMARC, DKIM, SMTP banner, reverse DNS (PTR/FCrDNS), DNSBL blacklists, STARTTLS and registration (WHOIS/RDAP) — with a plain-language verdict on why your mail lands in spam. DKIM can only be checked if you know the selector (the name before ._domainkey, e.g. google, k1, selector1) — leave it blank to skip DKIM.
Enter a domain (e.g. example.com) to audit its email DNS and registration.