Thundermail DNS checker
Check that a domain's DNS records match the Thundermail setup — and, if any are missing, get exactly what to enter in your DNS provider's panel.
Lookups run entirely in your browser via DNS-over-HTTPS — no
server, nothing is stored. Public resolvers cache results, so a freshly
added record can take a little while to show up here (switch resolver or
retry). The command-line version
(verify_thundermail_dns.py)
can query an authoritative nameserver directly to bypass that.