Moxtools runs at https://tools.xmox.nl, but you can easily run it locally
without the rate limiting.
Similar functionality is also included in mox as subcommands (cli).
Functionality
Analyse SMTP server settings for a domain, looking up information in DNS
(DNSSEC, MX, SPF, DMARC, TLSRPT, DANE, MTA-STS), and connecting to at most 2
SMTP servers.
Verify the DKIM signatures in a message.
Check SPF result for a given sending IP address for a given sender domain name.